1. Epidemiologic-Study Design
Dr. Bassam Hijawi
Consultant , Epidemiologist
MOH , Jordan
Define the subject matter
Introduce yourself
Give housekeeping information (location of restrooms, break policy, etc)
Find out any relevant background and interest of the audience

2. By the end of this presentation , you will be able to know about :
Different types of Epid. Study design (Research )
Differences between Descriptive & Analytical design
Differences between types of Analytical design .
Examples of verbs to use are:
Explain
Describe
Calculate
Analyze
Prepare
Design

3. Epidemiologic - Study Design
Descriptive epidemiologic studies.
Analytical epidemiologic studies.

4. Epidemiologic Study Design - Observational :. no Hypothesis
Epidemiologic Study Design - Observational : .no Hypothesis *cross Sectional Survey (prevalence Survey ) .Hypothesis *Analytical Studies *Ecological Studies -Experimental(unethical to perform experiments on people if exposure is harmful)

5. Descriptive Studies - Review
Populations:
- (correlational or ecological studies)
Individuals
Case reports
Case series
Cross-sectional surveys
Optional slide-delete if irrelevant to your topic

6. Analytic Studies Observational
Cohort studies (prospective)
Case-control studies (Retrospective)
Experimental (intervention or clinical trial)
Optional slide-delete if irrelevant to your topic

7. Descriptive Studies Populations (correlational or ecological studies)
Individuals
Case reports
Case series
Cross-sectional surveys

8. Correlational or Ecological Studies
It is type of descriptive study
Based on aggregate measures of exposure and outcome from several populations.
The population is the unit of observation available for study.
Exposures:
What percent of a population smokes?
What percent of 1-year old children are vaccinated against measles?
What percent of a population has piped water?

9. Correlational or Ecological Studies
Based on aggregate measures of exposure and outcome from several populations.
Outcome:
What percentage of a population died from MI?
What percentage of children had measles last year?
What percentage of population had episodes of diarrhea?

10. Correlational or Ecological Studies
Advantages
Easy to do
Use available data (“administrative” or other aggregate data)
Generate hypotheses for additional study

11. Correlational or Ecological Studies
Disadvantages
Unable to examine data for individuals
No assurance that persons with exposure are the same ones with the outcome
Ecologic fallacy
Unable to adjust for confounding factors

12. Descriptive Studies Populations (correlational or ecological studies)
. Individuals
Case reports
Case series
Cross-sectional surveys

13. Case reports The individual is the unit of observation
Clinical case with “unusual” clinical picture
May suggest an etiological association

14. Case series
First case report may stimulate compilation of additional case reports….a case series
(e.g. occurrence of Pneumocystis carinii among a group of young, homosexual men with no history of immune deficiency)

15. Case reports or Case series
Advantages:
Use available clinical data
Detailed individual data
Suggest need for investigation (hypothesis generation)
Disadvantages:
May reflect experience of one person or one clinician
No explicit comparison group

16. Descriptive Studies Populations (correlational or ecological studies)
Individuals
Case reports
Case series
Cross-sectional surveys

17. Cross-sectional Surveys (prevalence Study )
Collection of data on several individuals at “one point” in time.
Examples:
national census
community survey
survey of a particular group of persons (e.g., occupational group, school children)

18. Flow Diagram of C.S Study
N____S____ EC EC EC EC

19. Cross-sectional Surveys
Advantages
Standardized data collection tool.
Able to focus data collection in specific locations or specific groups of persons.
May make comparsions among study participants.
Relatively quick to do.
May be repeated to get data on trends.

20. Cross-sectional Surveys
Disadvantages
May be biased by lack of participation
Reflects prevalent, not incident cases

21. Analytic Studies Experimental (intervention or clinical trial)
Observational
Cohort studies (Follow up , Incidence , Panel or prospective )
Case-control studies (case – referent, case-history , trohoc or etrospective)
Optional slide-delete if irrelevant to your topic

22. What is a cohort? Marching towards outcomes
Group of individuals
sharing same experience
followed up for specified period of time
Examples
birth cohort
cohort of guests at wedding reception
Jordan FETP fourth cohort

23. Cohort Study
Investigator selects individuals on the basis of exposure status.
Exposure may have begun in past.
Investigator “follows up” the study participants to record occurrence of a particular event (outcome).
Compare rates of disease occurrence among exposed and unexposed groups of persons.
Optional slide-delete if irrelevant to your topic

24. Design of an Cohort Study
Individuals
“choose” their
exposure status
Source: partially adapted from WHO, 1993

25. Terminology: Retrospective or Prospective?
Suggest use the terms “retrospective” or “prospective” to refer to the timing of events in relation to initiation of study. (Hennekens and Buring, 1987)
Retrospective cohort study: exposure and disease have occurred prior to start of study
Prospective cohort study: disease has not occurred prior to start of study

26. Cohort Study: Advantages
Calculate incidence rates (attack rates)
Clear definition of temporal sequence
Well-suited to study result of a rare exposure
Able to identify adequate numbers of exposed and unexposed persons

27. Strengths of cohort studies
Strengths of cohort studies *can directly measure incidence in exposed and unexposed groups -true relative risk *well suited for rare exposure *temporal relationship exposure- disease is clear *less subject of selection biases outcome Not known (prospective )

28. Cohort Study: Advantages
Allows examination of multiple effects of exposure
If prospective, minimizes bias in:
Selection, since enrollment is completed without knowledge of disease outcome
exposure measurement

29. Cohort Study: Disadvantages
Inefficient for diseases with long latency period
If prospective, expensive and time consuming
If retrospective, requires availability of adequate records.
Loss of participants during follow-up period
Not suitable for rare diseases (large sample)
Exposure can change
Multiple exposure = difficult
Expensive and time consuming

30. Analytic Studies Experimental (intervention or clinical trial)
Observational
Cohort studies (prospective)
Case-control studies (retrospective)
Optional slide-delete if irrelevant to your topic

31. Case-control Study
Investigator selects individuals on the basis of disease status.
May use incident or prevalent cases
Investigator assess the exposure history of study participants.
Compare odds of exposure among persons with disease to odds of exposure among persons without disease.
Optional slide-delete if irrelevant to your topic

32. Design of a Case-control Study
Source: partially adapted from WHO, 1993

33. Case-control Study: Advantages
Well-suited to study result of rare diseases
Study of diseases with a long latency period
Efficient use of time and resources
Able to identify adequate numbers of affected and unaffected persons
Able to study a wide range of potential etiologic exposures

34. Case-control Study: Disadvantages
*cant compute directly relative risk
*not suitable for rare exposure
*temporal relationship exposure- disease difficult to establish.
*loss of precision due to sampling
*Not efficient for rare exposures
*biases +++
control selection
recall bias when collecting data

35. What kind of study design would you use in an outbreak investigation?
Cohort? Why?
Case-control? Why?
Other design ? Why ?

36. Choice of study design depends on:
Nature of disease under investigation
Type of exposure
Available resources

37. Experimental (intervention or clinical trial)
Investigator assigns determines who is exposed
Investigator “follows up” the study participants to record occurrence of a particular disease (or clinical treatment outcome)
Optional slide-delete if irrelevant to your topic

38. Experimental (intervention or clinical trial)
Could be based on individual or community level
Exposure could be assigned in a random or a non-random manner
Compare rates of outcome

39. Design of an Experimental Study
Investigator
Determines
Exposure Status
Source: partially adapted from WHO, 1993

40. The cohort study is the gold- standard of analytical Epidemiology

41. Recap
List Describe the differences between and descriptive and analytic studies.
Describe the differences between and experimental and observational studies
Tip! This should be a repeat of slide two. While this may seem redundant, it emphasizes to the learner what s/he has gained from the session & gives you opportunity to review and catch final questions.
Also summarize and make sure they understand where this fits in the ‘big picture’. You can do this in the form of questions. Ex. “So when you are assessing the validity of a test, which of these formulas will you be sure to calculate?”

42. Recap Describe different types of observational studies.
Describe the advantages and disadvantages descriptive and analytical studies.

43. Thank you Dr.Bassam