Observational Study Designs in Epidemiology NANA

8/11/2019 Observational Study Designs in Epidemiology NANA

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Angelica Kresnamurti

Bagian Farmakologi-Fakultas Farmasi

Unika Widya Mandala Surabaya


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Overview of scientific

method

Study sample

Conclusion about scientifictheory

(Causation)

Statistical inference

Biological inference

Conclusion about a population(Association)


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Types of Error

Random error Random variation, unsystematic

Bias Systematic variation

A consistent manner in which two study groups aretreated or evaluate differentlycan mask trueassociation

Interviewer bias, recall bias, etc

Confounding

A variable other than the risk factor and outcomeunder study which is related independently to boththe risk factor and the outcome variable and whichmay create an apparent association or mask a realone


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Epidemiological Study Designs

Observational

No human intervention

Experimental

Intervention

DescriptiveAttempt to uncover and portray the

occurrence of condition or problem

Analytical Determine the causes of the condition or

problem


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Epidemiological Study Designs

Uncontrolled assignmentControlled assignment

Experimental studies Observational studies

Community

assignment

Individual

assignment

Descriptive Analytical

Cross-sectional Sampling with

regard todisease

Sampling with

regard toexposure

Case-control Cohort

Community trial Clinical trial


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Study Designs in

Observational Epidemiology

1. Case reports and case series

2. Cross sectional studies

3. Case-control studies

4. Cohort studies


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Data Collection

Cross-sectional study

Data collection occurs only once

Data analysisidentify subjects with certain diseases &

exposures

Case-control

Data had been recorded before the study was initiated

The direction of inquiry is back in time

Exposures have occurred beforehand

Data analysisidentify subjects with certain diseases &

exposures


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Data Collection

Cohort The direction of inquiry is mostly forward in time

Data collection and recording occur (multiple times)throughout the length of the study exposure &

development of disease identified Cross sectional study to identify study subject

Retrospective cohort study Data have been recorded before the study began

Investigator revisited subjects after the study hasbeen initiatedcollected new data while the studyis in progress to supplement the previously collecteddata


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Retrospective & Prospective Designs

Comparison

Retrospective Inexpensive to conduct

Completed in a shortertime period

Easier to access a largernumber of subjects

Allow results to beobtained more quickly

Useful for studyingexposure that no longeroccur

Information and data maybe less complete andinaccurate

Subject may not rememberpast information

Prospective

Expensive to conduct

Completed over a longertime period

More difficult to access

subjects and usuallyrequires a larger numberof subjects

Exposure status anddiagnostic methods fordisease may change

Loss of subjects from thestudy over time may besubstantial

Information and data maybe more complete andaccurate

Direct access to studysubjects enhances


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Case reports and Case

seriesCase reports A descriptive study of a single patient Provide

unusual medical occurrences

identify new diseases describe adverse effects form drug therapies challenge-rechallenge data to help establishcausality

No incidence data Low-cost approach

Case series A collection of case reports No control group


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Cross-sectional study

A prevalence study

A basic descriptive study

Examine relationships between a

disease or drug use problem and other

characteristics of people in a population

at one point in time


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Cross-Sectional Study

Design Advantages

Single data collection

Less expensive

Easier to conduct

Disadvantages Cannot show cause-effect relationships

Not effective if the level of disease rate is very small

Seasonal variations of disease are not wellrepresented

Limited value in predicting future occurrence ofsome disease

Less effective in identifying communicable diseasesof short incubation periods and short durations


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Case-control study

Analytical

Retrospective

Compares

people who have the disease or problem (cases) to those who do not (control)

With respect to exposure or characteristics of

interest (i.e. potential cause)

To identify factors that could be responsible forthe development of a disease or drug use

problem


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Case-control study

Advantages

Fewer subjects are needed

Smaller sample size

Lower cost

Possible to study several risk factor from a single disease

Practical for studying chronic disease with long latency periods

Disadvantages

Cases & controls are not representative for the whole population

No incidence prevalence

Inefficient where exposure is rare Possible bias in subject recall, exclusion criteria, determining that

the exposure precedes disease, and bias in selection criteria


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Case-control study

Selecting cases and controls

Case definition = specifying criteria for

defining a person as a case (having the

disease)

Eligibility criteria = a set of criteria for

inclusion & exclusion of the study


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Case-control study

Matching cases & controls

To control confounding and selection bias

Helps to ensure that the groups are similar with respect toimportant risk factors

Advantages Increase statistical efficiency

Can achieve a specified level of statistical power with a smallersample size

Disadvantages Time consuming & expensive

Potential cases & controls may be excluded because matched cannot be made

Unmatched cases & controls must be discarded Matched variables cannot be evaluated as risk factors in the study

population

Continuous matching categories may too broad, residual casecontrol differences may persist


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Cohort study

An incidence study

Measures characteristics or attributes in a

population free of disease or drug use

problem relates them to subsequent of the disease in

that population as it is followed over time

A longitudinal study

Performed when intentional exposure of

human beings cannot be justified


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Cohort study

Advantages Provide information on incidence of disease Show temporal relationship between exposure and

disease Appropriate for the study of rare exposure

The best observational study for establishing cause-effect relationship

Disadvantages Time consuming Expensive

Not efficient for studying rare disease Losses to follow up ~ validity Changes over time in diagnostic methods,

exposures, study population ~ bias


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Cohort study

Retrospective cohort study

Uses information on prior to exposure anddisease status

Advantages All of the events have occurred

Conclusion can be drawn more rapidly

Lower cost

Possible for an exposure that no longer occur (i.e.

discontinued medical treatments) Disadvantages

Rely on existing records or subject recall


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Cohort study

Potential bias

Bias in assessment of the outcome

Information bias

Biases form nonresponse and losses to

follow up

Analytic bias


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References

Gordis L. 2002. Epidemiology. 2nded. WBSaunders Company. p 131-157

Greenberg RS, Daniels SR, Flanders WD,Eley JW, Boring JR. 2001. Medical

Epidemiology. 3rded. McGraw Hill. p 113-140

Strom BL. 2000. Pharmacoepidemiology.3rded. John Wiley & Sons Ltd. p 17-29

Waning B, Montagne M. 2001.Pharmacoepidemiology: Principles andPractice. McGraw Hill. p 45-62


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Observational Study Designs in Epidemiology NANA

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