PowerPoint Presentation

TEACH-VIP

T rainin= g,

E ducating,

A dvancing

C ollaboration in

H ealth on

V iolence and

I njury

P revention =

Core curriculum

Lesson 6

= The materials in this lesson are based on an injury prevention and control curriculum originally = developed by the World Health = Organization and a global network = of injury experts.

Gen= eral lesson description

Fundam= ental epidemiological concepts such as causality and inference, risk, exposure,= and bias and confounding will be considered in the first part of this lesson.=

The fo= llowing section will focus on study designs used in epidemiological research.

A clas= sification of epidemiological study designs is presented.

Three = common descriptive study designs (case report, case series and the descriptive epidemiological study) for research and evaluation on injuries are explai= ned and compared in this lecture.

Other = important analytic study designs will be covered in Lesson 7 including the randomiz= ed controlled trial, which is considered the “gold standard” of scientific research design.

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General aspects on methods for studying and evaluating injury prevention co= ntrol and safety promotion interventions

Studyi= ng injuries: research methods I

Lesso= n 6 = Secti= on III. General study techniques for injury prevention and control, and safety promo= tion

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Main objectiv= e of this lesson

=
To introduce studen= ts to the fundamental principles of epidemiology and the methodologies used = in epidemiological research that can be applied to injury = prevention and cont= rol, and safety promotion.

Core competen= cies that students should attain by the end of the = session <= /span>
<= /span>

1. To gain an under= standing of:

fundamental epidemiological concepts such as causal= ity and

inference, risk, exposure, bias and confounding;= 3;

<= /span>

different types of descriptive study designs used in injury prevention

research such as case reports, case series and descriptive

epidemiological studies.

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Studying injuries:

research methods I

TEACH-VIP

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Epidemiology

•Definition:
•study of patterns and causes of diseases and <= /span>injuries in h= uman populations
•

•Approach:
•determining association between a particular <= /span>= factor and injury = •if association exists, th= en determining nature of association (causal or non-causal)

Def= inition of epidemiology (1)

Epidem= iology is the study of patterns and causes of diseases and injuries in human population= s. Epidemiologists are concerned with the numbers and types of illnesses and injuries, the groups of people in which these occur, and the factors that influence their distribution.

Implic= it in this definition is the idea that illness and injury are not random occurrences, and therefore, it is possible to identify those groups and individuals mo= st at risk of illness or injury. Further, the field of epidemiology encompas= ses the application of this knowledge to the control of health problems.

Epi= demiological approach and reasoning (1)

Epidem= iology is a comparative discipline involving the study of illness and injury at diffe= rent time periods and places, and among different types of people. It can be applied to both infectious and non-infectious conditions, including injur= y.

There = are basically two steps in the epidemiological approach:

The de= termination of a statistical association between a particular characteristic and = the disease or injury of interest.

If an = association is shown, then determining whether the association is causal or no= n-causal follows.

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Non-causal relationships

FACTOR:

frailty

CHARACTE= RISTIC:

heart disease

CONDITION:
fall injury

OBSERVED:
association&#= 13;

Cau= sality and inference (1)

An obs= erved statistical relationship may be either real or not real. If the relations= hip is not real then the observation is usually the result of bias in the stu= dy, that is, something has occurred which has resulted in a deviation of the results from the truth (2). Bias will be discussed later in this lesson.<= /font>

If a r= elationship is real, then it may be either non-causal or causal.

Non= -causal relationships (1)

These = exist where the association between a particular characteristic and condition (diseas= e or injury) is mediated by another factor. For example, heart disease and fal= ls resulting in injury could be observed to be associated. However, the fact= or operating as the causal factor for the condition (in this case a fall resulting injury) could be frailty, which could also be associated with h= eart disease.

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Causal relationship

CHARACTE= RISTIC:

elevated blood alcohol

CONDITION = (disease/injury):

motor vehicle crash injury

Cau= sal relationships (1)

A caus= al relationship is one where the characteristic is directly related to the condition (disease or injury).

There = are a number of criteria, which may be used as guides for establishing causality. The first four criteria may be thought of as necessary for, and the remainder= as strengthening the case for, causality.

The ca= use must always precede the effect in time.

The ca= use must be correlated with the effect.

The co= rrelation must be large enough that it is unlikely to be due to chance alone.

The re= search design must be adequate to rule out indirect relationships and confounding.

The me= chanism of causation must be plausible in terms of what is already known.

The pr= esence of a dose-response relationship is a good indicator of cause. A dose-response relationship in one in which a change in exposure results in a change in = the risk of the specified outcome.

The re= lationship is consistently observed in different groups, places and times.

The ca= use is specific for the condition.

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Risk

•50% had dizziness

•3% had cognitive

impairment

Older people who did not fall <= /span>

•50% had dizziness

•15% had cognitive = ; &n= bsp;

impairment

Older people who fell

Hypothetical study of risk factors for falls among older people:

Ris= k (1)

Risk i= s the probability that an individual with a certain characteristic will develop= a condition (disease or injury). The particular characteristics associated = with an increased probability of developing a condition are known as risk fact= ors. The identification of risk factors is a central feature of epidemiological research.

The im= portance of a control group in the identification of risk factors is shown in the table above. In a study of risk factors for falls among older people, using onl= y a group of older people who fell could lead to the identification of dizzin= ess, but exclude cognitive impairment, as a risk factor. However, the importan= ce of a control group of older people who did not fall is clear and the conclusion would be reversed: cognitive impairment but not dizziness, is identified as a risk factor.

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Exposure

= RISK OF = INJURY

TIME SPENT RIDING <= /span>(EXPOSURE) = ;

Hypothesis: Increased time spent (exposure) bi= cycle riding increases risk of injury

Exp= osure (1)

Exposu= re is an important concept in epidemiological studies. Exposure is a measure of the amount (in terms of duration or intensity) of a factor, which may either = be a risk or protective factor, to which an individual or group has been subjected.

In inj= uries, exposure to a particular injury is dependent on whether one is involved i= n a particular activity. Therefore one is not at risk of a motor vehicle inju= ry if one is not near a motor vehicle or to drowning if not near water. In t= he case of bicycling injuries, for example, bicycle riding is the risk factor and the hours of riding time (or the distance travelled) is the amount of exposure. In this case, a likely hypothesis is that as the hours of riding time (or the distance travelled) increase so does the risk of crash and injury.

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Bias

•Non-random error that results in an untrue estimate of an exposure’s effect on the risk of injury

•May occur in the design, conduct or analysis stage of a study

•Various types & sources of bias

–e.g. selection bias

Bia= s (1)

Bias i= n epidemiology refers to non-random error that results in an untrue estimate of an exposure’s effect on the risk of disease or injury. The error may o= ccur due to the design, conduct or analysis of a study.

Variou= s types and sources of bias have been identified. One example is selection bias. Supp= ose in a study of risk factors for childhood injury occurring in the home, ca= ses were being selected form a particular hospital. This feature could be the source of selection bias, depending on the area being served by that hospital. If, for example, the hospital served a middle to upper class community, who are well educated and have relatively high incomes, it is likely that the housing will be newer and better maintained. This has the potential to bias the results as the group who are selected for the study= are likely to differ, on important characteristics, from those who are not selected.

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Confounding

characteristic:

alcohol consumption

injury:

drowning

youth

(confounder)

inability to swim (confounder)

Confounding in a hypothetical study of alcohol consumption as a risk factor for drowning

Con= founding (1)

Confou= nding refers to the situation in which the measure of risk associated with a particular factor is distorted due to the association with other factors that influe= nce the disease/injury outcome (2).

In a s= tudy of whether characteristic X is a risk factor for the disease/injury Y, Z is a confounder if:

it is = a risk factor for the disease/injury Y;

it is = associated with the characteristic X, but not as a result of exposure to characteris= tic X.

Confou= nding may be illustrated by a hypothetical study of alcohol consumption as a risk fact= or for drowning (see above):

firstl= y, other known or likely risk factors, such as inability to swim, are potential confound= ers of the study;

second= ly, factors associated with alcohol consumption but not a result of it, such as age, = are potential confounders.

Confou= nding can be controlled for either in the study design or in the analysis phase if the necessary information is collected during the study.

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Research and surveillance

<= span style=3D'font-family:Arial'>• Effective epidemiolog= ical analysis requires data

<= span style=3D'font-family:Arial;visibility:hidden'>•

• Most information avai= lable on injuries identified through

= injury surveillance systems

<= span style=3D'font-family:Arial;visibility:hidden'>•

<= span style=3D'font-family:Arial'>• Surveillance can help answer the question

- “What is the problem?” <= /div>
•<= /span> <= /span>

<= span style=3D'font-family:Arial'>• Research can help ans= wer the questions

- “What are the risk and protective factors?”

- “What is/are the cause/s?”

<= span style=3D'font-family:Arial'>• It helps to propose solutions and test their effectiveness

<= span style=3D'font-family:Arial;visibility:hidden'>•

<= span style=3D'font-family:Arial'>• Guidance for decision-makers

As sho= wn in the previous lessons, good reliable data is important for effective epidemiological analysis. Information from surveillance systems can be us= eful for defining problems or developing questions, which form the basis for epidemiological studies. However, many countries do not have well-develop= ed injury surveillance, or vital registration systems, so other methods may = be required such as household surveys and verbal autopsies to provide base information.

The re= search process attempts to answer questions or establish associations between certain conditions or events and certain outcomes (injuries). This research proce= ss also contributes to generate new questions or to evaluate interventions. = It is a powerful tool to guide decision-makers and the community as a whole = (3).

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•Questions to ask:

•Description or hypothesis testing?

•Can exposure be manipulated by the investigator?
•How often and how soon does one expect to observe the outcome of interest?

•Are there important local opportunities or barriers?

•

•

Choosing a research design

The ty= pe of research design one chooses to answer a particular research question depends on a number of factors. Questions to consider in choosing a research design include:

does t= he primary research aim involve description or hypothesis testing?

can a subject’s exposure to a potential casual or protective factor be manipulated by the investigator?

how of= ten and how soon does one expect to observe the outcome of interest?

are th= ere important local opportunities or barriers?

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Focus of injury epidemiology

Descrip= tion= 3;

•<= /span> Identify the distribution of injur= ies

= according to cause or demographic= s= 3;

=

= For example:

= - all injuries in a population

= - subset of the population<= /span>

Analysi= s= 3;

•<= /span> Assessing if risk of injury is dif= ferent for individuals exposed to &nb= sp;

= different risk factors

= For example:

= Does absence of a helmet increase/decrease risk of death?

Epidem= iology can focus on the description of situations, populations or events, or on the analysis and establishment of causal or potentially causal associations.<= /font>

Des= criptive epidemiology helps to determine the magnitude of a problem by documen= ting clinical severity and by yielding rates, if based on all cases in a population. Descriptive studies can also help identify the distribution of injuries according to a specific cause or demographic characteristics. Descriptive studies, for example, can focus on identifying all injuries i= n a population or injuries in a subset of the population, e.g. children.

Ana= lytic epidemiology goes a step further to determine whether or not the risk= of injury is different for individuals exposed to a given risk factor or set= of risk factors compared to those who were not exposed. It can also provide estimates of changes in risk after implementing different interventions.<= /font>

These = two epidemiological approaches work together to inform best practice in the prevention or control of injuries. By providing a means to understand both the frequency in which the events occur (through surveillance and descrip= tive studies), and risk factors that lie behind their occurrence (through anal= ytic epidemiological studies), these studies can guide researchers and decision-makers on their task to find or design the best possible prevent= ive practices.

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Study desi= gn types

Study designs

Descriptive

Analytic

Case report

Other

Case series

Descriptive <= span lang=3DEN-AU style=3D'font-family:Arial;font-size:67%'>epidemiological study=

Ethnographic study=

Observational

Intervention

Randomized controlled trial
Quasi-experimental=

Cohort study

Case-control study=

Cross-sectional study=

Longitudinal designs

Other

Retrospective

Prospective

Before-after

Interrupted time series<= /span>

Other

Source: Koepsall, 2001.

The ab= ove figure presents a classification of epidemiological study designs (4).

Des= criptive study designs include case series, case reports and descriptive epidemiolog= ical studies.

Ana= lytic study designs include both observational and intervention studies.

Observ= ational studies include cross-sectional studies, case-control studies, cohort and longitudinal designs.

Interv= ention studies are randomized controlled trials and quasi-experimental studies.

These = methods are widely used in science and in public health. The following sections will explore some of these commonly used descriptive methods for research in injuries. Lesson 7 will discuss analytic study designs. The methods are presented from the simplest to the most complex and real examples of their use are provided.

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Types of descriptive studies

<= span style=3D'font-family:Arial;font-size:133%'>• Case reports
<= span style=3D'font-family:Arial;font-size:133%;visibility:hidden'>•<= /span> =

<= span style=3D'font-family:Arial;font-size:133%'>• Case series
<= span style=3D'font-family:Arial;font-size:133%;visibility:hidden'>•<= /span> =

<= span style=3D'font-family:Arial;font-size:133%'>• Descriptive epidemiological studie= s

Des= criptive epidemiology provides clues about the magnitude of a problem and its distribution within populations. Study designs include case reports, case series and descriptive epidemiological studies.

Descri= ptive studies can be used in many ways. These include the documentation of a previously unknown event or set of events and the establishment of the frequency and magnitude of an injury occurrence within a population. This helps to determine the frequency of specific injury outcomes, and to identify new hypotheses to test in analytic studies. They may also include the study of the opportunities and barriers that exist within a population for control= ling or preventing injuries.

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Case reports and case series

Series of cases

Describe a pa= ttern of injuries amon= g a group of = individuals in terms of their exposure and injury outcomes

= Define the magnitude and distribution of the problem and may generate hypotheses for future analytic research

Individual case

Describes an individual’s own exposure and injury outcome

The fi= rst, and most simple descriptive, method used, is the case report that focuses o= n a narrative statement of an injury occurrence that is perhaps unusual. These single descriptions can alert others about a potential hazard when groupe= d in what is known as a case series, and can provide indications of new questions to be answered by more formal research methodologies.

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Source: Patterns of Homicide - Cali, Colombia 1993-1994. MMWR 1995; 44:734-7

Case series applied&#= 13;

Cases of violence-related injury transported by ambulance service<= /span>

= Describes pattern of injuries in terms of age, cause, locality and mortality

= Also compares mortality on days of political strike versus days without political str= ike

At least some violence related to politics

= Detailed study of causes explaining role of political and ethnic tension may suggest strategies to lessen violence

Source: Chotani et al., 2002.

This s= tudy describes a case series of violence-related injuries that were transported by an ambulance service in Karachi, Pakistan, over a three-year period, between 1993–1996 (5).

Object= ives

Govern= ment reports on violence in developing countries are almost universally based upon pol= ice data, which are typically incomplete and unreliable. Violence in Karachi = was evaluated using ambulance service, not police, records.

Settin= g

Karach= i, Pakistan.

Method= ology

The st= udy was based on a case series of persons suffering from intentional injuries and transported by Edhi, the largest emergency service in Karachi, between October 1993 and January 1996. Main outcome variables were injury and dea= th rates.

Result= s

Edhi A= mbulance Service transported 4091 intentionally injured persons during the 29-month period from October 1993 to January 1996. Of the total, 95% (n =3D 3864) = were males; 74% (n =3D 2823) were 20 to 40 years of age, and 2400 (58%) died b= efore reaching the hospital. Firearms were the most common mode of injury (n =3D 3396, 83%). A large proportion, 46% (n =3D 1828), of violent injuries occ= urred in four neighbourhoods of Karachi: 22% in Korangi (n =3D 884) and 8% each= in Orangi (n =3D 337), Malir Colony (n =3D 307), and Nazimabad (n =3D 300). = On the 32 days when a political strike was called, more people were injured (mean = =3D 10.4 v 5.0 persons, P =3D 0.01) and killed (mean 6.6 v 3.9 persons= , P<0.01) compared with days without a political strike.

Conclu= sion

Violen= ce is a major public health problem in Karachi, affecting predominantly wage earners. At least some of the violence is rooted within the political system. Detailed study of the causes of violence that explains the role that political and ethnic tensions play, may suggest strategies to lessen the toll of violen= ce.

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Descriptive epidemiological studies

Description of characteristics

of population, injuries and event=

Defined Population

= Injury cases within the population

PERSON

PLACE

TIME

A d= escriptive epidemiological study uses a set of cases that are representative of a population (also known as population-based). It describes the frequency a= nd characteristics of an injury problem and permits a more accurate calculat= ion of frequency of events including incidence, prevalence and mortality rates (6).

This d= iagram explains the structure of a descriptive epidemiological study. This type = of study combines data on a population-based set of cases with denominator d= ata and is often used when little is known about the frequency and risk facto= rs associated with an injury. Most descriptive epidemiological studies rely = on data from existing sources such as state-wide trauma registries, mortality registration systems or hospital administrative datasets. However, primary data collection may be necessary in areas where no such data sources exis= t.

The cl= assic conceptual framework of descriptive epidemiology is person, place and tim= e. Injury frequency is compared across (4):

per= son (sub-populations)

based = on age, gender, race, income, or other socio-demographic factors;

pla= ce

geogra= phic areas or rural versus urban settings;

tim= e

long-t= erm secular trends in injury occurrence, variations in terms of time of day, day of w= eek, month of year or season.

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Descriptive epidemiological studies =

Description of characteristics

of population, injuries, event an= d outcomes

Population of= Uganda

Survey of representative sample of population in urban and rural settings<= /div>

Age

Gender<= span lang=3DEN-AU style=3D'font-family:Arial;color:#3333CC;mso-color-index:5; mso-special-format:lastCR;display:none'>

Urban vs rural

5 preceding years

Source: Kobusingye et al., 2001. <= span lang=3DEN-AU style=3D'font-family:Arial;mso-ascii-font-family:Arial;mso-bi= di-font-family: "Times New Roman";font-size:67%;mso-special-format:lastCR;display:none'>&#= 13;

In Uga= nda, most injury information is contained in police records but this generally cons= ists of traffic- and violence-related injuries. Data from mortuaries had simil= ar limitations. To gain an understanding of the overall pattern of injury in Uganda, Kobusingye, Guwatudde & Lett (7) undertook community surveys = in urban and rural areas in 1997 and 1998.

Object= ives

To des= cribe and contrast injury patterns in rural and urban Uganda.

Settin= gs

One ru= ral and one urban community in Uganda.

Method= s

Commun= ity health workers interviewed adult respondents in households selected by multistage= sampling, using a standardized questionnaire.

Result= s

In the= rural setting, 1673 households, with 7427 persons, were surveyed. Injuries had = an annual mortality rate of 92/100 000 persons, and disabilities a prevalence proportion of 0.7%. In the urban setting 2322 households, with 10 982 peo= ple, were surveyed. Injuries had an annual mortality rate of 217/100 000, and injury disabilities a prevalence proportion of 2.8%. The total incidence = of fatal, disabling, and recovered injuries was 116/1000/year. Leading cause= s of death were drowning in the rural setting, and road traffic in the city.

Conclu= sion

Injuri= es are a substantial burden in Uganda, with much higher rates than those in most Western countries. The urban population is at a higher risk than the rural population, and the patterns of injury differ. Interventions to control injuries should be a priority in Uganda.

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General lesson description
Fundamental epidemiological concepts such as causality and inference, risk, exposure, and bias and confounding will= be considered in the first part of this lesson. The following section will focus on study designs used in epidemiological research.= 3;
A classification of epidemiological study designs is presented.
Three common descriptive study designs (case report, case series and the descriptive epidemiological study) for research and evaluation on injuries are explained and compared in this lecture. Other import= ant analytic study designs will be covered in Lesson 7 including the randomized controlled trial, which = is considered the “gold standard” of scientific research design.

Definition of epidemiology (1)
Epidemiology is the study of patterns and causes of diseases and injuries in human populations. Epidemiologists are concerned with the numbers and types of illnesses and injuries, the groups of people in which these occur, and the factors = that influence their distribution. Implicit in this definition is the idea that illness and injury are= not random occurrences,= and therefore, it is possible to identify those groups and individuals most at risk of illness or injury. Further, the field of epidemiology encompasses the application of this knowledge to the control of health problems. =
Epidemiological approach and reasoning (1)
Epidemiology is a comparative discipline involving the study of illness and injury at different time periods and places, and among different types of people. It can be applied to both infectious and non-infectious conditions, including injury.
There are basically two steps in the epidemiological approach:
The determination = of a statistical associati= on between a particular characteristic and the disease or injur= y of interest. If an association is shown, then determining whether the association is <= span lang=3DEN-GB style=3D'font-family:Arial;mso-ascii-font-family:Arial;mso-bi= di-font-family: Arial;mso-hansi-font-family:Arial'>causal or non-causal follows.

Causality and inference (1)
An observed statistical relationship may be either real or not real. If the relationship is not real then the observation is usually the result of bias in the study, that is, something has occurred which has resulted in a deviation of the results from the truth (2). Bias will be discussed later in this lesson.
If a relationship = is real, then it may be either non-causal or causal.

Non-causal relationships (1)
These exist where = the association between a particular characteristic and condition (disease or injury) is mediat= ed by another factor. For example, heart disease and falls resulting in injury could be observed to be= associated. However, the factor operati= ng as the causal factor for the condition (in this case a fall resulting injury) could be frailty, which could also be associated with heart disease.

Causal relationships (1)

A causal relationship is one where the characteristic is directly related to the condition (disease or injury).

There are a number of criteria, which m= ay be used as guides for establishing causality. The first four criteria may be thought of as necessary f= or, and the remainde= r as strengthening the case for, causality.

The cause must always precede the effec= t in time.

The cause must be correlated with the effect.

The correlation must be large enough th= at it is unlikely to be due to chance alone.

The research design must be adequate to rule out indirect relationships and confounding.

The mechanism of causation must be plausible in terms of what is already known.

The presence of a dose-response relationship is a good indicator of cause. A dose-response relationship in one in wh= ich a change in exposure results in a change in the risk of the specified outcome.

The relationship is consistently observ= ed in different groups, places and times.

The cause is specific for the condition= .

Risk (1)
Risk is the probability that an individual with a certain characteristic will <= span lang=3DEN-GB style=3D'font-family:Arial;mso-ascii-font-family:Arial;mso-bi= di-font-family: Arial;mso-hansi-font-family:Arial'>develop a condition (disease or injury). The particular characteristics associated with an increased probability of developing a condition = are known as risk factors. The identificati= on of risk factors is a central feature of epidemiological research. The importance of a control group in the identification of risk factors is shown in the table above. In a study of risk factors for falls among older people, using only a group of older people who fell could lead to the identification of dizziness, but exclude cognitive impairment, as a risk factor. However, the importance of a control gr= oup of older people who did not fall is clear and the conclusion would be reversed: cognitive impairment= but not dizziness, is identified as a risk factor.

Exposure (1)
Exposure is an important concept in epidemiological studies. Exposure is a measure of the amount (in terms of dura= tion or intensity) of a factor, which may either be a risk or protective factor, to which an individual or group has been subject= ed. In injuries, exposure to a particular injury is dependent on whether one is involved in a particular activity. Therefore one is not at risk of a motor vehicle injury if one is not near a mot= or vehicle or to drowning if not near water. In the case of bicycling injuries, for example, bicycle ridi= ng is the risk factor and t= he hours of riding time (or the distance travelled) is the amount of exposure. In this case, a likely hypothesis is that as the hours of riding time (or the distance travelled) increa= se so does the risk of crash and injury.

Bias (1)
Bias in epidemiolo= gy refers to non-random error that results in an untrue estimate of an exposure’s effect = on the risk of disease or injury. The error may occur due to the design, conduct or analysis of a study. Various types and sources of bias have been identified. One example= is selection bias. Suppose in a study of r= isk factors for childhood injury occurring in the home, cases were being selected form a particular hospital. This feature could be the source of selection bias, depending on the area being served by that hospital. If, for example, the hospital served a middle to upper class community, who are well educated and have relatively high incomes, it is likely that the housing will be newer and better maintained. This has the potential to bias the results as the group who are selected for the study are likely to differ, on important characteristics, from those who are not selected.

Confounding (1)
Confounding refers= to the situation in which the measure of risk associated with a particular factor is distorted d= ue to the association with other factors that influence the disease/injury outco= me (2). In a study of whether characteristic X = is a risk factor for the disease/injury Y, Z is a confounder if:
it is a risk factor for the disease/injury Y;
it is associated w= ith the characteristic X, but not as a result of exposure to characteristic X. Confounding may be illustrated by a hypothetical study of alcohol consumption as a risk factor for drowning (see above): <= span lang=3DEN-GB style=3D'font-family:Arial;mso-ascii-font-family:Arial;mso-bi= di-font-family: Arial;mso-hansi-font-family:Arial'>firstly, other known or likely risk factors, such as inability to swim, are potential confounders of the study; = ;secondly, factors associated with alcoh= ol consumption but not a result of it, such as age, are potential confounders. Confounding can be controlled for eithe= r in the study design or in the analysis phase if the necessary information is collected during the study.

As shown in the previous lessons, good reliable data is important f= or effective epidemiological analysis. Information from surveillance systems can be useful for defining problems or developing questions, which form the basis for epidemiological studies. However, many countries do not h= ave well-developed injury surveillance, or vital registration systems, so other methods may be required such as household surveys and verbal autops= ies to provide base information. The research process attempts to answer questions or establish associations between certain conditions or events and certain outco= mes (injuries). This research process also contributes to generate new questions or to evaluate interventions. It is a powerful tool to guide decision-makers and the community as a whole (3).

The type of research design one chooses to answer a particular rese= arch question depends o= n a number of factors. Questions to consider in choosing a research design include:
does the primary research aim involve description or hypothesis testing?
can a subject̵= 7;s exposure to a potential casual or protective factor be manipulated by the investigator? how often and how soon does one expect = to observe the outcome of interest?
are there important local opportunities or barriers?

Epidemiology can focus on the description of situations, population= s or events, or on the analysis and establishment of causal or potentially causal associations. Descriptive epidemiology<= span lang=3DEN-GB style=3D'font-family:Arial;mso-ascii-font-family:Arial;mso-bi= di-font-family: Arial;mso-hansi-font-family:Arial'> helps to determine the magnitude of a problem by documenti= ng clinical severity and by yielding rates, if based on all cases in a population. Descriptive studies can also help identify the distribution of injuries according to a specific cause = or demographic characteristics. Descriptive studies, for example, can focus on identifying all inju= ries in a population or injuries in a subset of the population, e.g. children. Analytic epidemiology goes a step further to determine wheth= er or not the risk of inju= ry is different for individuals exposed to a given risk factor or set of risk factors compared to those who were= not exposed. It can also provide estimates of changes in risk after implementing different interventions. These two epidemiological approaches work together to inform best practice in the prevention or control of injuries. By providing a means to understand both the frequency in which the events occur (through surveillance and descriptive studies), and risk factors that lie behind their occurr= ence (through analytic epidemiological studies), these studies can guide researchers and decision-makers on their task to find or design the best possible preventive practices.

The above figure presents a classification of epidemiological study designs (4).<= span lang=3DEN-GB style=3D'font-family:Arial;mso-ascii-font-family:Arial;mso-bi= di-font-family: Arial;mso-hansi-font-family:Arial'> Descriptive study designs= include case series, case reports and = descriptive epidemiological studies. Analytic study designs include both observational and intervention studies. = 3;Observational studies include cross-sectional studies, case-control studies, cohort and longitudinal designs. Intervention studies are randomized controlled trials and quasi-experimental studies. These methods are widely used in science and in public health. The following sections will explore some of these commonly used descrip= tive methods for resear= ch in injuries. Lesson 7 will discuss analytic study designs. The methods are presented from= the simplest to the most complex and real examples of their use are provided. <= /div>
Descriptive epidemiology provides clues about the magnitude of = a problem and its distribution within populations. Study designs include case reports, case series and descriptive epidemiological studies. Descriptive studies can be used in many ways. These include the documentation of a previously unknown e= vent or set of events and the establishment of the frequency and magnitude of an injury occurrenc= e within a population. This helps to determine the frequency of specific injury outcomes, and to identify new hypothese= s to test in analytic studies. They may also include the study of the opportunities and barriers that e= xist within a population= for controlling or preventing injuries.

The first, and most simple descriptive, method used, is the = case report that focuses on a narrative statement of an injury occurrence that is perhaps unusual. These single descriptions can alert others about a potenti= al hazard when grouped= in what is known as a case series, and can provide indications of new questions to be answered by more formal research= methodologies.

This study describes a case series of violence-related injuries that were transported by an ambulance service in Karachi, Pakistan, over a three-= year period, between 1993–1996 (5).

Objectives

Government reports on violence in developing countries are almost universally based upon police data, which are typically incomplete and unreliable. Violence in Karachi was evaluated using ambulance service, not police, records.

Setting

Karachi, Pakistan.&n= bsp;

Methodology

The study was based on a case series of persons suffe= ring from intentional injuries and transported by Edhi, the largest emergency service in Karachi, between October 1993 and January 1996. Main outcome variables were injury and death rates.
Results

Edhi Ambulance Service transported 4091 intentionally injured persons during the 29-month period from October 1993 to January 1996. Of the tota= l, 95% (n =3D 3864) were males; 74% (n =3D 2823) were 20 to 40 years of age, and 2400 (58= %) died before reaching the hospital. Firearms were the most common mode of injury (n =3D 3= 396, 83%). A large proportion, 46% (n =3D 1828), of violent injuries occurred in four neighbourhoods of Karachi: 22% in Korangi (n =3D 884) and 8% each in Orangi (n =3D 337), Malir Col= ony (n =3D 307), and Nazimabad (n =3D 300). On the 32 days when a political strike was called, mo= re people were injured (mean =3D 10.4 v 5.0 persons, PP

Conclusion

Violence is a major public health problem in Karachi, affecting predominantly wage earners. At least some of the violence is rooted within the political system. Detailed study of the causes of violence that explains the role that politi= cal and ethnic tensions play, may suggest strategies to lessen the toll of violence.

A descripti= ve epidemiological study uses a set of cases that are representative of a population (also known as population-based). It= describes the frequency and characteris= tics of an injury problem and permits a more accurate calculation of frequency of events including incide= nce, prevalence and mortality rates (6). This diagram explains the structure of a descriptive epidemiological study. This type of study combines data on a population-based set of cases with denominator data and is often used when little is known about the frequency and risk factors associated with an injury. Most descriptive epidemiological studies rely= on data from existing sources such as state-wide trauma registries, mortality registration syst= ems or hospital administrative datasets. However, primary data collection may be necessary in areas where no such data sources exist. The classic conceptual framework of descriptive epidemiology is person, place and time. Injury frequency is compared across (4):
person (sub-populations)

based on age, gend= er, race, income, or other socio-demographic factors;

place

geographic areas or rural versus urban settings;

time=
long-term secular trends in injury occurrence, variations in terms of time of day, day of week, month of year or seas= on.

In Uganda, most injury information is contained in po= lice records but this generally consists of traffic- and violence-related injuries. Data from mortuaries had similar limitations. To gain an understanding of the overall pattern of injury in Uganda, Kobusingye, Guwatudde & Lett (7) undertook community surveys in urban and rural ar= eas in 1997 and 1998.
Objectives
To describe and contrast injury patterns in rural and urban Uganda.

Settings

One rural and one urban community in Uganda.

Methods
Community health workers interviewed adult respondents in households selected by multistage sampling, usin= g a standardized questionnaire.
Results
In the rural setting, 1673 households, with 7427 persons, were surveyed. Injuries had an annual mortality rate of 92/100 000 persons, and disabilities a prevalence proportion of 0.7%. In the urban setting 2322 households, with 10 982 people, were surveyed. Injuries had an annual mortality r= ate of 217/100 000, and injury disabilities a prevalence proportion of 2.8%. The total incide= nce of fatal, disabling, and recovered injuries was 116/1000/year. Leading causes of death w= ere drowning in the rural setting, and road traffic in the city.
Conclusion Injuries are a substantial burden in Uganda, with much higher rates than those in most Western countries. The ur= ban population is at a higher risk than the rural population, and the patterns of injury differ. Interventions to control injuries should be a priority in Uganda.<= /span>
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sld.style.visibility=3D"visible" return } if( MakeNotesVis() ) return runAnimations =3D _InitAnimations(); =09 if( IsWin("PPTSld") ) parent.SldUpdated(GetSldId()) g_origSz=3DparseInt(SlideObj.style.fontSize) g_origH=3Dsld.style.posHeight g_origW=3Dsld.style.posWidth g_scaleHyperlinks=3D(document.all.tags("AREA").length>0) if( g_scaleHyperlinks ) InitHLinkArray() if( g_scaleInFrame||(IsWin("PPTSld") && parent.IsFullScrMode() ) ) document.body.scroll=3D"no" _RSW() if( IsWin("PPTSld") && parent.IsFullScrMode() ) FullScrInit(); =09 MakeSldVis(); ChkAutoAdv() if( runAnimations ) { if( document.all("NSPlay") ) document.all("NSPlay").autoStart =3D false; if( sld.filters && sld.filters.revealtrans ) setTimeout( "document.body.start()", sld.filters.revealtrans.duration * = 1000 ); else document.body.start(); } } function MakeSldVis()=20 { var fTrans=3Dg_showAnimation && SldHasTrans() if( fTrans )=09 { if( g_bgSound ) { idx=3Dg_bgSound.indexOf(","); pptSound.src=3Dg_bgSound.substr( 0, idx ); pptSound.loop=3D -(parseInt(g_bgSound.substr(idx+1))); } SlideObj.filters.revealtrans.Apply()=09 } SlideObj.style.visibility=3D"visible" if( fTrans ) SlideObj.filters.revealtrans.Play() } function MakeNotesVis()=20 { if( !IsNts() ) return false=20 SlideObj.style.display=3D"none" nObj =3D document.all.item("NotesObj") parent.SetHasNts(0) if( nObj ) {=20 nObj.style.display=3D"" parent.SetHasNts(1) } return 1 } function ChkAutoAdv() { if(SldHasTrans()) SlideObj.onfilterchange=3DAutoAdv else AutoAdv() } function AutoAdv() { if(!IsWin("PPTSld") || !gUseSldTimings )return var sld=3DGetCurSld() if( (sld.mAdvDelay>0) && !parent.IsFramesMode() ) setTimeout("parent.GoToNextSld()",sld.mAdvDelay) } function GetObj(id) { if(g_supportsPPTHTML) return document.all(id); else return document.getElementById(id); } function SldHasTrans() { return SlideObj.style.filter !=3D ""; } function GetSldId()=20 { var regExp =3D /file:\/\/\//i var pos =3D location.href.search(regExp) if (MHTMLPrefix !=3D "" && pos !=3D -1) sId =3D location.href.substring(pos) else { sId =3D RemoveFilePrefixFromHref(location.href); var regExp =3D /\// var fixedHref =3D sId var pos =3D -1 =09 pos =3D fixedHref.search(regExp) while (pos !=3D -1) { fixedHref =3D fixedHref.replace(regExp, "\\") pos =3D fixedHref.search(regExp) } =09 if (g_fBaseHyperlink =3D=3D true) sId =3D "file:///" + fixedHref; else sId =3D fixedHref.substring(fixedHref.lastIndexOf('\\') + 1) } =09 return sId } function HideMenu() { if( frames["PPTSld"] && PPTSld.document.all.item("ctx= tmenu") && PPTSld.ctxtmenu.style.display!=3D"none" ) { PPTSld.ctxtmenu.styl= e.display=3D'none'; return true } return false } function IsWin( name ) { return window.name =3D=3D name } function IsNts() { return IsWin("PPTNts") } function IsSldOrNts() { return( IsWin("PPTSld")||IsWin("PPTNts") ) } function SupportsPPTAnimation() { return( navigator.platform =3D=3D "Win32"= && navigator.appVersion.indexOf("Windows")>0 ) } function SupportsPPTHTML() { var appVer=3Dnavigator.appVersion, msie=3DappVer.indexOf("MSIE "), ver=3D0 if( msie >=3D 0 ) ver=3DparseFloat( appVer.substring( msie+5, appVer.indexOf(";",msie) ) ) else ver=3DparseInt(appVer) return( ver >=3D 4 && msie >=3D 0 ) } function _RSW() { if( !g_supportsPPTHTML || IsNts() || ( !g_scaleInFrame && (!IsWin("PPTSld") || !parent.IsFullScrMode()) ) ) return var padding=3D0; if( IsWin("PPTSld") && parent.IsFramesMode() ) padding=3D6 cltWidth=3Ddocument.body.clientWidth-padding cltHeight=3Ddocument.body.clientHeight-padding factor=3D(1.0*cltWidth)/g_origW if( cltHeight < g_origH*factor ) factor=3D(1.0*cltHeight)/g_origH newSize =3D g_origSz * factor if( newSize < 1 ) newSize=3D1 s=3DSlideObj.style s.fontSize=3DnewSize+"px" s.posWidth=3Dg_origW*factor s.posHeight=3Dg_origH*factor s.posLeft=3D(cltWidth-s.posWidth+padding)/2 s.posTop=3D(cltHeight-s.posHeight+padding)/2 if( g_scaleHyperlinks ) ScaleHyperlinks( factor ) } function _InitAnimations() { animRuntimeInstalled =3D ''+document.body.localTime !=3D 'undefined'; isFullScreen =3D (window.name =3D=3D "PPTSld") && !parent.IsFramesMode(); g_animUseRuntime =3D g_showAnimation && animRuntimeInstalled && !(isFullSc= reen && parent.IsSldVisited()); if( g_animUseRuntime ) { collSeq =3D document.all.tags("seq"); if( collSeq !=3D null ) { for(ii=3D0;ii numSlds ) gSldJumpIdx =3D numSlds; if ( gSldJumpIdx >=3D 0 ) { if ( gSldJumpIdx =3D=3D 0 ) gSldJumpIdx =3D 1; var jumpTo =3D parseInt(gSldJumpIdx); gSldJump =3D 0; gSldJumpIdx =3D ""; win.GoToSld( parent.GetSldList().mList[jumpTo-1].mSldHref ) } } } function _KDH() { if( event.keyCode =3D=3D 8 ) { event.returnValue =3D 0; parent.GoToPrevSld(); } } function DocumentOnClick() { if( IsNts() || parent.HideMenu() ) return; if( ( g_allowAdvOnClick && !parent.IsFramesMode() ) || (event && (event.keyCode=3D=3D32) ) ) parent.GoToNextSld(); } var g_supportsPPTHTML =3D SupportsPPTHTML(), g_scaleInFrame =3D 1, gId=3D""= , g_bgSound=3D"", g_scaleHyperlinks =3D false, g_allowAdvOnClick =3D 1, g_showInBrowser = =3D 0, gLoopCont =3D 0, gUseSldTimings =3D 1; var g_showAnimation =3D g_supportsPPTHTML && SupportsPPTAnimation() && ( (w= indow.name=3D=3D"PPTSld" && !parent.IsFramesMode()) || g_showInBrowser );va= r g_animManager =3D null; var g_animUseRuntime =3D false; var g_animItemsToHide, g_animInteractiveItems, g_animSlideTime; var g_animMainSequence =3D null; var ENDSHOW_MESG=3D"End of slide show, click to exit.", SCREEN_MODE=3D"Fram= es", gIsEndShow=3D0, NUM_VIS_SLDS=3D20, SCRIPT_HREF=3D"script.js", FULLSCR_= HREF=3D"fullscreen.htm"; var gCurSld =3D gPrevSld =3D 1, g_offset =3D 0, gNtsOpen =3D gHasNts =3D gO= tlTxtExp =3D 0, gHasNarration =3D 0, gOtlOpen =3D true window.gPPTHTML=3DSupportsPPTHTML() var g_fBaseHyperlink =3D false; var gMainDoc=3Dnew Array(new hrefList("slide0001.htm",1,-1,1),new hrefList(= "slide0044.htm",1,-1,1),new hrefList("slide0045.htm",1,-1,1),new hrefList("= slide0016.htm",1,-1,1),new hrefList("slide0034.htm",1,-1,1),new hrefList("s= lide0035.htm",1,-1,1),new hrefList("slide0036.htm",1,-1,1),new hrefList("sl= ide0038.htm",1,-1,1),new hrefList("slide0041.htm",1,-1,1),new hrefList("sli= de0039.htm",1,-1,1),new hrefList("slide0040.htm",1,-1,1),new hrefList("slid= e0018.htm",1,-1,1),new hrefList("slide0042.htm",1,-1,1),new hrefList("slide= 0023.htm",1,-1,1),new hrefList("slide0043.htm",1,-1,1),new hrefList("slide0= 003.htm",1,-1,1),new hrefList("slide0019.htm",1,-1,1),new hrefList("slide00= 20.htm",1,-1,1),new hrefList("slide0030.htm",1,-1,1),new hrefList("slide003= 3.htm",1,-1,1)); /********************************************* Frameset functions These functions control slide navigation and state of the frameset. **********************************************/ function RemoveFilePrefixFromHref(href) { var regExp =3D /^file:\/\/\//i; return href.replace(regExp, "") } function FullScrInit() { g_allowAdvOnClick =3D GetCurSld().mAdvOnClk document.body.style.backgroundColor=3D"black" document.oncontextmenu=3Dparent._CM; document.onkeydown =3D _KDH; document.ondragstart=3DCancel document.onselectstart=3DCancel self.focus() } function Redirect( frmId ) {=09 var str=3Ddocument.location.hash,idx=3Dstr.indexOf('#'), sId=3DGetSldId() if(idx>=3D0) str=3Dstr.substr(1); if( window.name !=3D frmId && ( sId !=3D str) ) { obj =3D GetObj("Main-File") window.location.href=3Dobj.href+"#"+sId return 1 } return 0 } var MHTMLPrefix =3D CalculateMHTMLPrefix();=20 function CalculateMHTMLPrefix() { if ( document.location.protocol =3D=3D 'mhtml:') {=20 href=3Dnew String(document.location.href)=20 Start=3Dhref.indexOf('!')+1=20 End=3Dhref.lastIndexOf('/')+1=20 if (End < Start)=20 return href.substring(0, Start)=20 else=20 return href.substring(0, End)=20 } return ''; } function GetTags(base,tag) { if(g_supportsPPTHTML) return base.all.tags(tag); else return base.getElementsByTagName(tag); } function UpdNtsPane(){ if(frames["PPTNts"]) PPTNts.location.replace( MHTMLP= refix+GetHrefObj( gCurSld ).mNtsHref ) } function UpdNavPane( sldIndex ){ if(gNavLoaded) PPTNav.UpdNav() } function UpdOtNavPane(){ if(gOtlNavLoaded) PPTOtlNav.UpdOtlNav() } function UpdOtlPane(){ if(gOtlLoaded) PPTOtl.UpdOtl() } function SetHasNts( fVal ) { if( gHasNts !=3D fVal ) { gHasNts=3DfVal UpdNavPane() } } function ToggleOtlText() { gOtlTxtExp=3D!gOtlTxtExp UpdOtlPane() } function ClearMedia() { // Clear any sounds playing before launching another browser window. Other= wise, // in fullscreen mode, you'll continue to hear the sound in the frames mod= e. if (PPTSld.pptSound) PPTSld.pptSound.loop =3D 0; } function FullScreen() {=20 if ( PPTSld.g_animUseRuntime ) PPTSld.document.body.pause(); ClearMedia(); var href =3D ( document.location.protocol =3D=3D 'mhtml:') ? FULLSCR_HREF = : FULLSCR_HREF+"#"+GetHrefObj(gCurSld).mSldHref; if (MHTMLPrefix !=3D "") href =3D RemoveFilePrefixFromHref(href) if(PPTNav.event.ctrlKey) { var w =3D (window.screen.availWidth * 1.0) / 2.0 var h =3D w * (PPTSld.g_origH * 1.0) / PPTSld.g_origW win =3D window.open( MHTMLPrefix+href,null,"toolbar=3D0,resizable=3D1,top= =3D0,left=3D0," + "width=3D"+ w + ",height=3D" + h ); if( win.document.body && PPTSld.g_animUseRuntime ) win.document.body.PPTSldFrameset=3Dwindow; } else { win =3D window.open( MHTMLPrefix+href,null,"fullscreen=3Dyes" ); if( win.document.body && PPTSld.g_animUseRuntime ) win.document.body.PPTSldFrameset=3Dwindow; } } function ToggleVNarration() { rObj=3DPPTSld.document.all("NSPlay") if( rObj && !PPTSld.g_animUseRuntime ) { if( (rObj.playState =3D=3D 1)||(rObj.playState =3D=3D 0) ) rObj.Play() else if( rObj.playState =3D=3D 2 ) rObj.Pause() else return; } else if( PPTSld.g_animUseRuntime ) { narObj =3D PPTSld.document.all("narrationID") if( narObj ) narObj.togglePause() } } function GetCurSldNum() { =20 obj=3DGetHrefObj(gCurSld) if( obj.mOrigVis =3D=3D 1 ) return obj.mSldIdx else =20 return gCurSld } function GetNumSlds() { =20 if( GetHrefObj(gCurSld).mOrigVis =3D=3D 1 ) return GetSldList().mNumVisSlds; else return GetSldList().mList.length } function GetSldNum( href ) { for(ii=3D0; ii 1 ) PopSldList(); else if( !IsFramesMode() ) { if( gLoopCont ) GoToFirst() else EndShow() } } function GoToPrevSld() { ii=3DgCurSld-1 if( ii > 0 ) { obj=3DGetHrefObj(ii) while ( obj && ( obj.mVis =3D=3D 0 ) && ( ii>0 ) ) obj=3DGetHrefObj(--ii) if( ii =3D=3D 0 ) ii=3D1 GoToSldNum(ii) } } function GoToFirst(){ GoToSld( GetHrefObj(1).mSldHref ) } function GoToLast() { ii=3DGetSldList().mList.length if( ii !=3D gCurSld ) GoToSld( GetHrefObj(ii).mSldHref ) } function GoToSldNum( num ) { if( PPTSld.event ) PPTSld.event.cancelBubble=3Dtrue obj =3D GetHrefObj( num ) obj.mVis=3D1 gPrevSld=3DgCurSld gCurSld =3D num; =09 if (MHTMLPrefix !=3D "") PPTSld.location.replace(MHTMLPrefix+RemoveFilePrefixFromHref(obj.mSldHref= )) else PPTSld.location.replace(obj.mSldHref) =09 if( IsFramesMode() ) { UpdNavPane(); UpdOtlPane(); UpdNtsPane() } } function GoToSld( href ) { if( PPTSld.event ) PPTSld.event.cancelBubble=3Dtrue GetHrefObj( GetSldNum(href) ).mVis=3D1 if (MHTMLPrefix !=3D "") PPTSld.location.replace(MHTMLPrefix+RemoveFilePrefixFromHref(href)) else PPTSld.location.replace(href) } function SldUpdated( id ) { if( id =3D=3D GetHrefObj(gCurSld).mSldHref ) return gPrevSld=3DgCurSld gCurSld=3DGetSldNum(id) if( IsFramesMode() ) { UpdNavPane(); UpdOtlPane(); UpdNtsPane() } } function PrevSldViewed(){ GoToSld( GetHrefObj(gPrevSld).mSldHref ) } function HasPrevSld() { return ( gIsEndShow || ( gCurSld !=3D 1 && GetHrefO= bj( gCurSld-1 ).mVis =3D=3D 1 )||( GetCurSldNum() > 1 ) ) } function HasNextSld() { return (GetCurSldNum() !=3D GetNumSlds()) } function CloseWindow() { if( HideMenu() ) return; =09 var event =3D PPTSld.event; if( !IsFramesMode() && event && (event.keyCode=3D=3D27 || event.keyCode=3D= =3D32 || event.type=3D=3D"click" ) ) window.close( self ); CatchNumKeys( self, event ); } function Unload() { gIsEndShow=3D0; } function SetupEndShow() { gIsEndShow=3D1; PPTSld.document.body.scroll=3D"no"; PPTSld.document.onkeypress=3DCloseWindow; PPTSld.document.onclick=3DCloseWindow; PPTSld.document.oncontextmenu=3D_CM; } function EndShow() { if( IsFramesMode() ) return if( PPTSld.event ) PPTSld.event.cancelBubble=3Dtrue doc=3DPPTSld.document var dir =3D doc.body.dir if( dir !=3D "rtl" ) dir =3D "ltr"; doc.open() doc.writeln('

' + ENDSHOW_MESG + '
') doc.close() } function SetSldVisited(){ GetSldList().mList[gCurSld-1].mVisited=3Dtrue } function IsSldVisited(){ return GetSldList().mList[gCurSld-1].mVisited } function hrefList( sldHref, visible, advDelay, advClk ) { this.mSldHref=3D this.mNtsHref =3D sldHref this.mOrigVis=3D this.mVis =3D visible this.mVisited=3D false this.mAdvDelay=3D advDelay this.mAdvOnClk=3D advClk } function SldList(arr,curSld,fEnd) { this.mCurSld =3D curSld; this.mList =3D new Array(); var idx =3D 1; for(ii=3D0;ii 0) { PushSldList(sldList,fEnd); gCurSld =3D 1; } else if( PPTSld.event ) PPTSld.event.cancelBubble=3Dtrue } function PushSldList(arr,fEnd) { var ii =3D gSldStack.length; gSldStack[ii] =3D new SldList(arr,gCurSld,fEnd); GoToSld( gSldStack[ii].mList[0].mSldHref ); } function PopSldList() { if (gSldStack[gSldStack.length-1].fEndShow) EndShow() else { gCurSld =3D gSldStack[gSldStack.length-1].mCurSld; gSldStack[gSldStack.length-1] =3D null; gSldStack.length--; var sldList =3D gSldStack[gSldStack.length-1]; GoToSld( sldList.mList[gCurSld - 1].mSldHref ); } } var custShowList=3Dnew Array(); /********************************************* Navigation button implementation There are 2 types of buttons: ImgBtn, TxtBtn implemented as function objects. They share a similiar interface so the event handlers can call SetActive, for example, on a button=20 object without needing to know exactly=20 what type of button it is. **********************************************/ //---------------------------------- function ImgBtn( oId,bId,w,action ) //---------------------------------- { var t=3Dthis t.Perform =3D _IBP t.SetActive =3D _IBSetA t.SetInactive=3D _IBSetI t.SetPressed =3D _IBSetP t.SetDisabled=3D _IBSetD t.Enabled =3D _IBSetE t.ChangeIcon =3D null t.UserAction =3D action t.ChgState =3D _IBUI t.mObjId =3D oId t.mBorderId=3D bId t.mWidth =3D w t.mIsOn =3D t.mCurState =3D 0 } function _IBSetA() { if( this.mIsOn ) { obj=3Dthis.ChgState( gHiliteClr,gShadowClr,2 ) obj.style.posTop=3D0 } } function _IBSetI() { if( this.mIsOn ) { obj=3Dthis.ChgState( gFaceClr,gFaceClr,1 ) obj.style.posTop=3D0=20 } } function _IBSetP() { if( this.mIsOn ) { obj=3Dthis.ChgState( gShadowClr,gHiliteClr,2 ) obj.style.posLeft+=3D1; obj.style.posTop+=3D1 } } function _IBSetD() { =20 obj=3Dthis.ChgState( gFaceClr,gFaceClr,0 ) obj.style.posTop=3D0=20 } function _IBSetE( state ) { var t=3Dthis GetObj( t.mBorderId ).style.visibility=3D"visible" if( state !=3D t.mIsOn ) { t.mIsOn=3Dstate if( state ) t.SetInactive() else t.SetDisabled() } } function _IBP() { var t=3Dthis if( t.mIsOn ) { if( t.UserAction !=3D null ) t.UserAction() if( t.ChangeIcon ) { obj=3DGetObj(t.mObjId) if( t.ChangeIcon() ) obj.style.posLeft=3Dobj.style.posLeft+(t.mCurState-4)*t.mWidth else obj.style.posLeft=3Dobj.style.posLeft+(t.mCurState-0)*t.mWidth } t.SetActive() } =20 } function _IBUI( clr1,clr2,nextState ) { var t=3Dthis SetBorder( GetObj( t.mBorderId ),clr1,clr2 ) obj=3DGetObj( t.mObjId ) obj.style.posLeft=3Dobj.style.posLeft+(t.mCurState-nextState)*t.mWidth-obj= .style.posTop t.mCurState=3DnextState return obj } //----------------------------------------- function TxtBtn( oId,oeId,action,chkState ) //----------------------------------------- { var t=3Dthis t.Perform =3D _TBP t.SetActive =3D _TBSetA t.SetInactive=3D _TBSetI t.SetPressed =3D _TBSetP t.SetDisabled=3D _TBSetD t.SetEnabled =3D _TBSetE t.GetState =3D chkState t.UserAction =3D action t.ChgState =3D _TBUI t.mObjId =3D oId t.m_elementsId=3D oeId t.mIsOn =3D 1 } function _TBSetA() { var t=3Dthis if( t.mIsOn && !t.GetState() ) t.ChgState( gHiliteClr,gShadowClr,0,0 ) } function _TBSetI() { var t=3Dthis if( t.mIsOn && !t.GetState() ) t.ChgState( gFaceClr,gFaceClr,0,0 ) } function _TBSetP() { if( this.mIsOn ) this.ChgState( gShadowClr,gHiliteClr,1,1 ) } function _TBSetD() { =20 this.ChgState( gFaceClr,gFaceClr,0,0 ) this.mIsOn =3D 0 } function _TBSetE() { var t=3Dthis if( !t.GetState() ) t.ChgState( gFaceClr,gFaceClr,0,0 ) else t.ChgState( gShadowClr,gHiliteClr,1,1 ) t.mIsOn =3D 1 } function _TBP() { var t=3Dthis if( t.mIsOn ) {=20 if( t.UserAction !=3D null ) t.UserAction() if( !t.GetState ) return if( t.GetState() ) t.SetPressed() else t.SetActive() } =20 } function _TBUI( clr1,clr2,lOffset,tOffset ) { SetBorder( GetObj( this.mObjId ),clr1,clr2 ) Offset( GetObj( this.m_elementsId ),lOffset,tOffset ) } function Offset( obj, top, left ){ obj.style.top=3Dtop; obj.style.left=3Dle= ft } function SetBorder( obj, upperLeft, lowerRight ) { s=3Dobj.style; s.borderStyle =3D "solid" s.borderWidth =3D 1=20 s.borderLeftColor =3D s.borderTopColor =3D upperLeft s.borderBottomColor=3D s.borderRightColor =3D lowerRight } function GetBtnObj(){ return gBtnArr[window.event.srcElement.id] } function BtnOnOver(){ b=3DGetBtnObj(); if( b !=3D null ) b.SetActive() } function BtnOnDown(){ b=3DGetBtnObj(); if( b !=3D null ) b.SetPressed() } function BtnOnOut(){ b=3DGetBtnObj(); if( b !=3D null ) b.SetInactive() } function BtnOnUp() { b=3DGetBtnObj() if( b !=3D null ) b.Perform() else Upd() } function GetNtsState(){ return parent.gNtsOpen } function GetOtlState(){ return parent.gOtlOpen } function GetOtlTxtState(){ return parent.gOtlTxtExp } function NtsBtnSetFlag( fVal ) { s=3Ddocument.all.item( this.m_flagId ).style s.display=3D"none" if( fVal ) s.display=3D"" else s.display=3D"none" } function _BSetA_Border(){ b =3D gBtnArr[this.mObjId]; if( b !=3D null ) b.S= etActive() } function _BSetI_Border(){ b =3D gBtnArr[this.mObjId]; if( b !=3D null ) b.S= etInactive() } function _BSetP_Border(){ b =3D gBtnArr[this.mObjId]; if( b !=3D null ) b.S= etPressed() } function _BSetA_BorderImg() {=20 b =3D gBtnArr[this.mBorderId]=20 if( b !=3D null && this.mIsOn && !b.GetState() ) { obj=3Dthis.ChgState( gHiliteClr,gShadowClr,2 ) obj.style.posTop=3D0 } } function _BSetI_BorderImg() {=20 b =3D gBtnArr[this.mBorderId] if( b !=3D null && this.mIsOn && !b.GetState() ) { obj=3Dthis.ChgState( gFaceClr,gFaceClr,1 ) obj.style.posTop=3D0 } } var gHiliteClr=3D"THREEDHIGHLIGHT",gShadowClr=3D"THREEDSHADOW",gFaceClr=3D"= THREEDFACE" var gBtnArr =3D new Array() gBtnArr["nb_otl"] =3D new TxtBtn( "nb_otl","nb_otlElem",parent.ToggleOtlPan= e,GetOtlState ) gBtnArr["nb_otlElem"] =3D new TxtBtn( "nb_otl","nb_otlElem",parent.ToggleOt= lPane,GetOtlState ) gBtnArr["nb_nts"] =3D new ImgBtn( "nb_nts","nb_ntsBorder",10,parent.ToggleN= tsPane ) gBtnArr["nb_nts"].SetActive =3D _BSetA_BorderImg; gBtnArr["nb_nts"].SetInactive =3D _BSetI_BorderImg; gBtnArr["nb_ntsBorder"] =3D new TxtBtn( "nb_ntsBorder","nb_ntsElem",parent.= ToggleNtsPane,GetNtsState ) gBtnArr["nb_ntsElem"] =3D new TxtBtn( "nb_ntsBorder","nb_ntsElem",parent.To= ggleNtsPane,GetNtsState ) gBtnArr["nb_prevBorder"] =3D gBtnArr["nb_prev"]=3D new ImgBtn( "nb_prev","n= b_prevBorder",30,parent.GoToPrevSld ) gBtnArr["nb_nextBorder"] =3D gBtnArr["nb_next"]=3D new ImgBtn( "nb_next","n= b_nextBorder",30,parent.GoToNextSld ) gBtnArr["nb_sldshw"]=3D new ImgBtn( "nb_sldshw","nb_sldshwBorder",18,parent= .FullScreen ) gBtnArr["nb_sldshwBorder"] =3D new TxtBtn( "nb_sldshw","nb_sldshwBorder",pa= rent.FullScreen,null ) gBtnArr["nb_sldshwBorder"].SetActive =3D _BSetA_Border; gBtnArr["nb_sldshwBorder"].SetInactive =3D _BSetI_Border; gBtnArr["nb_sldshwText"] =3D new TxtBtn( "nb_sldshw","nb_sldshwText",parent= .FullScreen,null ) gBtnArr["nb_sldshwText"].SetActive =3D _BSetA_Border; gBtnArr["nb_sldshwText"].SetInactive =3D _BSetI_Border; gBtnArr["nb_voice"] =3D gBtnArr["nb_voiceBorder"] =3D new ImgBtn( "nb_voice= ","nb_voiceBorder",18,parent.ToggleVNarration ) gBtnArr["nb_otlTxtBorder"] =3D gBtnArr["nb_otlTxt"]=3D new ImgBtn( "nb_otlT= xt","nb_otlTxtBorder",23,parent.ToggleOtlText ) gBtnArr["nb_ntsBorder"].m_flagId=3D "nb_nts" gBtnArr["nb_ntsBorder"].SetFlag =3D NtsBtnSetFlag gBtnArr["nb_otlTxt"].ChangeIcon=3D GetOtlTxtState /********************************************* Context menu implementation _CM() is the function that's hooked up to the oncontextmenu event. Once we're asked to show the menu, we first build it by creating DIVs on-the-fly. Then we position it=20 within the screen area so it doesn't get clipped. Creating the DIVs using createElement() means we don't have to write out any extra HTML into the slide HTML files. **********************************************/ var sNext=3D"Next",sPrev=3D"Previous",sEnd=3D"End Show",sFont=3D"Arial",sAr= row=3D"Arrow",sFreeform=3D"Freeform",sRect=3D"Rectangle",sOval=3D"Oval" function ShowMenu() { BuildMenu(); var doc=3DPPTSld.document.body,x=3DPPTSld.event.clientX+doc.scrollLeft,y= =3DPPTSld.event.clientY+doc.scrollTop m =3D PPTSld.document.all.item("ctxtmenu") m.style.pixelLeft=3Dx if( (x+m.scrollWidth > doc.clientWidth)&&(x-m.scrollWidth > 0) ) m.style.pixelLeft=3Dx-m.scrollWidth m.style.pixelTop=3Dy if( (y+m.scrollHeight > doc.clientHeight)&&(y-m.scrollHeight > 0) ) m.style.pixelTop=3Dy-m.scrollHeight m.style.display=3D"" } function _CM() { if( !parent.IsFullScrMode() ) return; if(!PPTSld.event.ctrlKey) { ShowMenu() return false } else HideMenu() } function BuildMenu() { if( PPTSld.document.all.item("ctxtmenu") ) return var mObj=3DCreateItem( PPTSld.document.body ) mObj.id=3D"ctxtmenu" mObj.style.visibility=3D"hidden" var s=3DmObj.style s.position=3D"absolute" s.cursor=3D"default" s.width=3D"120px" SetCMBorder(mObj,"menu","black") var iObj=3DCreateItem( mObj ) SetCMBorder( iObj, "threedhighlight","threedshadow" ) iObj.style.padding=3D2 CreateMenuItem( iObj,sNext,M_GoNextSld,M_True ) CreateMenuItem( iObj,sPrev,M_GoPrevSld,M_HasPrevSld ) =09 CreateSeparator( iObj ) CreateMenuItem( iObj,sEnd,M_End,M_True ) mObj.style.visibility=3D"visible" } function Cancel() { window.event.cancelBubble=3Dtrue; window.event.returnVa= lue=3Dfalse } function Highlight() { ChangeClr("activecaption","threedhighlight") } function Deselect() { ChangeClr("threedface","menutext") } function Perform() { e=3DPPTSld.event.srcElement if( e.type=3D=3D"menuitem" && e.IsActive() ) e.Action() else PPTSld.event.cancelBubble=3Dtrue } function ChangeClr( bg,clr ) { e=3DPPTSld.event.srcElement if( e.type=3D=3D"menuitem" && e.IsActive() ) { e.style.backgroundColor=3Dbg e.style.color=3Dclr } } function M_HasPrevSld() { return( parent.HasPrevSld() ) } function M_GoNextSld() { if( gIsEndShow ) M_End(); else GoToNextSld() } function M_GoPrevSld() { if( gIsEndShow ) { gIsEndShow=3D0; history.back();= PPTSld.event.cancelBubble=3Dtrue; } else GoToPrevSld() } function M_True() { return true } function M_End() { window.close( self ) } function CreateMenuItem( node,text,action,eval ) { var e=3DCreateItem( node ) e.type=3D"menuitem" e.Action=3Daction e.IsActive=3Deval e.innerHTML=3Dtext if( !e.IsActive() ) e.style.color=3D"threedshadow" e.onclick=3DPerform e.onmouseover=3DHighlight e.onmouseout=3DDeselect s=3De.style; s.fontFamily=3DsFont s.fontSize=3D"9pt" s.paddingLeft=3D2 } function CreateSeparator( node ) { var sObj=3DCreateItem( node ) SetCMBorder(sObj,"menu","menu") var s=3DsObj.style s.borderTopColor=3D"threedshadow" s.borderBottomColor=3D"threedhighlight" s.height=3D1 s.fontSize=3D"0px" } function CreateItem( node ) { var elem=3DPPTSld.document.createElement("DIV") node.insertBefore( elem ) return elem } function SetCMBorder( o,ltClr,rbClr ) { var s=3Do.style s.backgroundColor=3D"menu" s.borderStyle=3D"solid" s.borderWidth=3D1 s.borderColor=3DltClr+" "+rbClr+" "+rbClr+" "+ltClr } ------=_NextPart_01C8328C.AB643320 Content-Location: file:///C:/2D693CD6/CoreLesson6_files/fullscreen.htm Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset="us-ascii" ------=_NextPart_01C8328C.AB643320 Content-Location: file:///C:/2D693CD6/CoreLesson6_files/notes_flag.gif Content-Transfer-Encoding: base64 Content-Type: image/gif R0lGODlhCgAKAPcAAAAAAIAAAACAAICAAAAAgIAAgACAgICAgMwENMTExPz8/AAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAMDAwP8AAAD/AP//AAAA//8A/wD//////ywAAAAACgAKAEAIKgDx4UNA sKDAgQUTJiCogGHDhBAfFlRAMSFCiAguTozYUGJEiAk0EhQYEAA7 ------=_NextPart_01C8328C.AB643320 Content-Location: file:///C:/2D693CD6/CoreLesson6_files/buttons.gif Content-Transfer-Encoding: base64 Content-Type: image/gif R0lGODlhWAESAPf4AAAAAIAAAACAAICAAAAAgIAAgACAgICAgAQEBISEBASEBISEhAQEhMTExAQE /KTM9Pz8/ERERPz8BAT8/KSkpGRkhMTcxCRkxAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAMDAwP8AAAD/AP//AAAA//8A/wD//////yH5BAEAAPgALAAAAABYARIA QAj/APEJHEiwoMGDCBMqXMiwocOHECNKnEixosWLGCEiQKCRo8YDIEHig2DxAD4LKD1avDDhgUuV GUOGbHBR5QGYFBG4fHAB58EKECJEwCfUYAWPFGAygLCRKQIIUKM6WAohKUGgCikcFWh1INWoYKVS 7SrQ41GbIhGYLAuVQVOoC+IyXUuUAkG1HE3KFDhAwkgJc5/qDZmxsOHDiBMrXsy4sePDGyP7lChT 5MULmDPnlDw5YmW6FTNrfgi0aNGEZPEtbfo2bNTUpYeeRph69dPWrqvCNFuBIGG1A59CYPAVQtwF cw0OxWdTIOiBCQAjaAB17fOFII8voGmRc+eOkilm/z9OvTtnjN4hYk1YoT3H2rnBOphPAB9skgq3 2lcaX/5YnJVt9BloAar12UEIRGCZdQghMABI1Tn32IQUVthYexhmqGGGMBHAgIfEhSiiiATAtOGJ GnYI4ogsEldicAYOGNJGZaml3Y0L3NTZUBz1xlB0PUoUI0jlVWRSVN89xBKSGB1YU1TMoRfVBEle hR9HQs1GEHxQ3RZZbveZthxt/LEmXHyp5XWABSCpaRJwbM13gAACPHVccgJFgF+NEhqUAEkQSCfc ddhVhh5dVTaEAEsTUNlkZUWKN9BNGDE6QU8OrSdbllzpxyVTTrU21Uj3scfhp7nNpyoDaTIEJ3P9 If8J2kbLNYegg9JRBwGhFvbq66+ZUiDssMQWK2yHxiZLrInKNotss8l+B5yBrr5p2UIJvortANoC 6+234IbLla/elRtZjeamh5CC3Sb0YLvixivvYkDFGlZqBNh7r4n6goVvv6/ZlCicN+kL71ALTnpQ dCIZp7CihkLA3UQmoWRBogyxtBPGCTnZncVR1rSTo5nuydC/Eo8kUH+lOoTyyvjoCuZu+PjYIKLD rZybtrM1d10C0QXKEVz48GrQkEeWdFJKlbb0UmEeV0SzyC6RvNB646LWIVjUNeC1zAFb+RDKXksM 9r531bwmpQW9+hQDDsx5pqwDRWBXcFES2hc+gEn/wJGdEEWdE6LoWcoxQweaTNmkhydkKaYMYY2Q p1unbLl/pPKbn3v7EZRvrKvqlja2ONvrtoIw9tn2g32/tQBlhtYkU+MNikZ7QYlPDPuMldpOmuJX nVo5VF3HjI+q89mteX5IDd/fVFClma5kiE4f2XUJhlz09gj2NbTDRifkmu7zXjR++RVJ/lPznuvr QH2iD6S+UewP9Dnon6d2NLwN8n90BB6hC68cFMCHoe+ACASP9c4DowUyEF0OPFcDI0ij/VXPaAKC UfhS95AKGoQ7IBRICI1HwhGaUIQoLGEKT6jCFrLwhSuMoQtlCMMZ2rCGOKShDm+4wxzy8Ic+DGIP B4cIRCKGMCAAOy== ------=_NextPart_01C8328C.AB643320 Content-Location: file:///C:/2D693CD6/CoreLesson6_files/frame.htm Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset="us-ascii" PowerPoint Presentation ------=_NextPart_01C8328C.AB643320 Content-Location: file:///C:/2D693CD6/CoreLesson6_files/outline.htm Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset="us-ascii"

No= tes

Slide Show

Outline

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"Definition= "

Definition:

study of patterns and causes of diseases and injuries in human populations

Approach:

determining association between a particular factor and injury

if association exists, then determining nature of association (causa= l or non-causal)

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"Non-rando= m error that results in..."

Non-random error that results in an untrue estimate of an exposure’s effect on the risk of injury

May occur in the design, conduct or analysis stage of a study

Various types & sources of bias

e.g. selection bias

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"Questions= to ask"

Questions to ask:

Description or hypothesis testing?

Can exposure be manipulated by the investigator?

How often and how soon does one expect to observe the outcome of interest?

Are there important local opportunities or barriers?

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	Gen= eral lesson description
	Fundam= ental epidemiological concepts such as causality and inference, risk, exposure,= and bias and confounding will be considered in the first part of this lesson.=
	The fo= llowing section will focus on study designs used in epidemiological research.
	A clas= sification of epidemiological study designs is presented.
	Three = common descriptive study designs (case report, case series and the descriptive epidemiological study) for research and evaluation on injuries are explai= ned and compared in this lecture.
	Other = important analytic study designs will be covered in Lesson 7 including the randomiz= ed controlled trial, which is considered the “gold standard” of scientific research design.


	Def= inition of epidemiology (1)
	Epidem= iology is the study of patterns and causes of diseases and injuries in human population= s. Epidemiologists are concerned with the numbers and types of illnesses and injuries, the groups of people in which these occur, and the factors that influence their distribution.
	Implic= it in this definition is the idea that illness and injury are not random occurrences, and therefore, it is possible to identify those groups and individuals mo= st at risk of illness or injury. Further, the field of epidemiology encompas= ses the application of this knowledge to the control of health problems.
	Epi= demiological approach and reasoning (1)
	Epidem= iology is a comparative discipline involving the study of illness and injury at diffe= rent time periods and places, and among different types of people. It can be applied to both infectious and non-infectious conditions, including injur= y.
	There = are basically two steps in the epidemiological approach:
	The de= termination of a statistical association between a particular characteristic and = the disease or injury of interest.
	If an = association is shown, then determining whether the association is causal or no= n-causal follows.


	Cau= sality and inference (1)
	An obs= erved statistical relationship may be either real or not real. If the relations= hip is not real then the observation is usually the result of bias in the stu= dy, that is, something has occurred which has resulted in a deviation of the results from the truth (2). Bias will be discussed later in this lesson.<= /font>
	If a r= elationship is real, then it may be either non-causal or causal.
	Non= -causal relationships (1)
	These = exist where the association between a particular characteristic and condition (diseas= e or injury) is mediated by another factor. For example, heart disease and fal= ls resulting in injury could be observed to be associated. However, the fact= or operating as the causal factor for the condition (in this case a fall resulting injury) could be frailty, which could also be associated with h= eart disease.


	Cau= sal relationships (1)
	A caus= al relationship is one where the characteristic is directly related to the condition (disease or injury).
	There = are a number of criteria, which may be used as guides for establishing causality. The first four criteria may be thought of as necessary for, and the remainder= as strengthening the case for, causality.
	The ca= use must always precede the effect in time.
	The ca= use must be correlated with the effect.
	The co= rrelation must be large enough that it is unlikely to be due to chance alone.
	The re= search design must be adequate to rule out indirect relationships and confounding.
	The me= chanism of causation must be plausible in terms of what is already known.
	The pr= esence of a dose-response relationship is a good indicator of cause. A dose-response relationship in one in which a change in exposure results in a change in = the risk of the specified outcome.
	The re= lationship is consistently observed in different groups, places and times.
	The ca= use is specific for the condition.


	Ris= k (1)
	Risk i= s the probability that an individual with a certain characteristic will develop= a condition (disease or injury). The particular characteristics associated = with an increased probability of developing a condition are known as risk fact= ors. The identification of risk factors is a central feature of epidemiological research.
	The im= portance of a control group in the identification of risk factors is shown in the table above. In a study of risk factors for falls among older people, using onl= y a group of older people who fell could lead to the identification of dizzin= ess, but exclude cognitive impairment, as a risk factor. However, the importan= ce of a control group of older people who did not fall is clear and the conclusion would be reversed: cognitive impairment but not dizziness, is identified as a risk factor.


	Exp= osure (1)
	Exposu= re is an important concept in epidemiological studies. Exposure is a measure of the amount (in terms of duration or intensity) of a factor, which may either = be a risk or protective factor, to which an individual or group has been subjected.
	In inj= uries, exposure to a particular injury is dependent on whether one is involved i= n a particular activity. Therefore one is not at risk of a motor vehicle inju= ry if one is not near a motor vehicle or to drowning if not near water. In t= he case of bicycling injuries, for example, bicycle riding is the risk factor and the hours of riding time (or the distance travelled) is the amount of exposure. In this case, a likely hypothesis is that as the hours of riding time (or the distance travelled) increase so does the risk of crash and injury.


	Bia= s (1)
	Bias i= n epidemiology refers to non-random error that results in an untrue estimate of an exposure’s effect on the risk of disease or injury. The error may o= ccur due to the design, conduct or analysis of a study.
	Variou= s types and sources of bias have been identified. One example is selection bias. Supp= ose in a study of risk factors for childhood injury occurring in the home, ca= ses were being selected form a particular hospital. This feature could be the source of selection bias, depending on the area being served by that hospital. If, for example, the hospital served a middle to upper class community, who are well educated and have relatively high incomes, it is likely that the housing will be newer and better maintained. This has the potential to bias the results as the group who are selected for the study= are likely to differ, on important characteristics, from those who are not selected.


	Con= founding (1)
	Confou= nding refers to the situation in which the measure of risk associated with a particular factor is distorted due to the association with other factors that influe= nce the disease/injury outcome (2).
	In a s= tudy of whether characteristic X is a risk factor for the disease/injury Y, Z is a confounder if:
	it is = a risk factor for the disease/injury Y;
	it is = associated with the characteristic X, but not as a result of exposure to characteris= tic X.
	Confou= nding may be illustrated by a hypothetical study of alcohol consumption as a risk fact= or for drowning (see above):
	firstl= y, other known or likely risk factors, such as inability to swim, are potential confound= ers of the study;
	second= ly, factors associated with alcohol consumption but not a result of it, such as age, = are potential confounders.
	Confou= nding can be controlled for either in the study design or in the analysis phase if the necessary information is collected during the study.


	As sho= wn in the previous lessons, good reliable data is important for effective epidemiological analysis. Information from surveillance systems can be us= eful for defining problems or developing questions, which form the basis for epidemiological studies. However, many countries do not have well-develop= ed injury surveillance, or vital registration systems, so other methods may = be required such as household surveys and verbal autopsies to provide base information.
	The re= search process attempts to answer questions or establish associations between certain conditions or events and certain outcomes (injuries). This research proce= ss also contributes to generate new questions or to evaluate interventions. = It is a powerful tool to guide decision-makers and the community as a whole = (3).


	The ty= pe of research design one chooses to answer a particular research question depends on a number of factors. Questions to consider in choosing a research design include:
	does t= he primary research aim involve description or hypothesis testing?
	can a subject’s exposure to a potential casual or protective factor be manipulated by the investigator?
	how of= ten and how soon does one expect to observe the outcome of interest?
	are th= ere important local opportunities or barriers?


	Epidem= iology can focus on the description of situations, populations or events, or on the analysis and establishment of causal or potentially causal associations.<= /font>
	Des= criptive epidemiology helps to determine the magnitude of a problem by documen= ting clinical severity and by yielding rates, if based on all cases in a population. Descriptive studies can also help identify the distribution of injuries according to a specific cause or demographic characteristics. Descriptive studies, for example, can focus on identifying all injuries i= n a population or injuries in a subset of the population, e.g. children.
	Ana= lytic epidemiology goes a step further to determine whether or not the risk= of injury is different for individuals exposed to a given risk factor or set= of risk factors compared to those who were not exposed. It can also provide estimates of changes in risk after implementing different interventions.<= /font>
	These = two epidemiological approaches work together to inform best practice in the prevention or control of injuries. By providing a means to understand both the frequency in which the events occur (through surveillance and descrip= tive studies), and risk factors that lie behind their occurrence (through anal= ytic epidemiological studies), these studies can guide researchers and decision-makers on their task to find or design the best possible prevent= ive practices.


	The ab= ove figure presents a classification of epidemiological study designs (4).
	Des= criptive study designs include case series, case reports and descriptive epidemiolog= ical studies.
	Ana= lytic study designs include both observational and intervention studies.
	Observ= ational studies include cross-sectional studies, case-control studies, cohort and longitudinal designs.
	Interv= ention studies are randomized controlled trials and quasi-experimental studies.
	These = methods are widely used in science and in public health. The following sections will explore some of these commonly used descriptive methods for research in injuries. Lesson 7 will discuss analytic study designs. The methods are presented from the simplest to the most complex and real examples of their use are provided.


	Des= criptive epidemiology provides clues about the magnitude of a problem and its distribution within populations. Study designs include case reports, case series and descriptive epidemiological studies.
	Descri= ptive studies can be used in many ways. These include the documentation of a previously unknown event or set of events and the establishment of the frequency and magnitude of an injury occurrence within a population. This helps to determine the frequency of specific injury outcomes, and to identify new hypotheses to test in analytic studies. They may also include the study of the opportunities and barriers that exist within a population for control= ling or preventing injuries.


	The fi= rst, and most simple descriptive, method used, is the case report that focuses o= n a narrative statement of an injury occurrence that is perhaps unusual. These single descriptions can alert others about a potential hazard when groupe= d in what is known as a case series, and can provide indications of new questions to be answered by more formal research methodologies.


	This s= tudy describes a case series of violence-related injuries that were transported by an ambulance service in Karachi, Pakistan, over a three-year period, between 1993–1996 (5).
	Object= ives
	Govern= ment reports on violence in developing countries are almost universally based upon pol= ice data, which are typically incomplete and unreliable. Violence in Karachi = was evaluated using ambulance service, not police, records.
	Settin= g
	Karach= i, Pakistan.
	Method= ology
	The st= udy was based on a case series of persons suffering from intentional injuries and transported by Edhi, the largest emergency service in Karachi, between October 1993 and January 1996. Main outcome variables were injury and dea= th rates.
	Result= s
	Edhi A= mbulance Service transported 4091 intentionally injured persons during the 29-month period from October 1993 to January 1996. Of the total, 95% (n =3D 3864) = were males; 74% (n =3D 2823) were 20 to 40 years of age, and 2400 (58%) died b= efore reaching the hospital. Firearms were the most common mode of injury (n =3D 3396, 83%). A large proportion, 46% (n =3D 1828), of violent injuries occ= urred in four neighbourhoods of Karachi: 22% in Korangi (n =3D 884) and 8% each= in Orangi (n =3D 337), Malir Colony (n =3D 307), and Nazimabad (n =3D 300). = On the 32 days when a political strike was called, more people were injured (mean = =3D 10.4 v 5.0 persons, P =3D 0.01) and killed (mean 6.6 v 3.9 persons= , P<0.01) compared with days without a political strike.
	Conclu= sion
	Violen= ce is a major public health problem in Karachi, affecting predominantly wage earners. At least some of the violence is rooted within the political system. Detailed study of the causes of violence that explains the role that political and ethnic tensions play, may suggest strategies to lessen the toll of violen= ce.


	A d= escriptive epidemiological study uses a set of cases that are representative of a population (also known as population-based). It describes the frequency a= nd characteristics of an injury problem and permits a more accurate calculat= ion of frequency of events including incidence, prevalence and mortality rates (6).
	This d= iagram explains the structure of a descriptive epidemiological study. This type = of study combines data on a population-based set of cases with denominator d= ata and is often used when little is known about the frequency and risk facto= rs associated with an injury. Most descriptive epidemiological studies rely = on data from existing sources such as state-wide trauma registries, mortality registration systems or hospital administrative datasets. However, primary data collection may be necessary in areas where no such data sources exis= t.
	The cl= assic conceptual framework of descriptive epidemiology is person, place and tim= e. Injury frequency is compared across (4):
	per= son (sub-populations)
	based = on age, gender, race, income, or other socio-demographic factors;
	pla= ce
	geogra= phic areas or rural versus urban settings;
	tim= e
	long-t= erm secular trends in injury occurrence, variations in terms of time of day, day of w= eek, month of year or season.


	In Uga= nda, most injury information is contained in police records but this generally cons= ists of traffic- and violence-related injuries. Data from mortuaries had simil= ar limitations. To gain an understanding of the overall pattern of injury in Uganda, Kobusingye, Guwatudde & Lett (7) undertook community surveys = in urban and rural areas in 1997 and 1998.
	Object= ives
	To des= cribe and contrast injury patterns in rural and urban Uganda.
	Settin= gs
	One ru= ral and one urban community in Uganda.
	Method= s
	Commun= ity health workers interviewed adult respondents in households selected by multistage= sampling, using a standardized questionnaire.
	Result= s
	In the= rural setting, 1673 households, with 7427 persons, were surveyed. Injuries had = an annual mortality rate of 92/100 000 persons, and disabilities a prevalence proportion of 0.7%. In the urban setting 2322 households, with 10 982 peo= ple, were surveyed. Injuries had an annual mortality rate of 217/100 000, and injury disabilities a prevalence proportion of 2.8%. The total incidence = of fatal, disabling, and recovered injuries was 116/1000/year. Leading cause= s of death were drowning in the rural setting, and road traffic in the city.
	Conclu= sion
	Injuri= es are a substantial burden in Uganda, with much higher rates than those in most Western countries. The urban population is at a higher risk than the rural population, and the patterns of injury differ. Interventions to control injuries should be a priority in Uganda.

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5	"Definition= " Definition: study of patterns and causes of diseases and injuries in human populations Approach: determining association between a particular factor and injury if association exists, then determining nature of association (causa= l or non-causal)
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10	"Non-rando= m error that results in..." Non-random error that results in an untrue estimate of an exposure’s effect on the risk of injury May occur in the design, conduct or analysis stage of a study Various types & sources of bias e.g. selection bias
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13	"Questions= to ask" Questions to ask: Description or hypothesis testing? Can exposure be manipulated by the investigator? How often and how soon does one expect to observe the outcome of interest? Are there important local opportunities or barriers?
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