1. 1 NOVEMBER 2003 Design 1-11-03 1 Overview of Epidemiological Study

3. Formulate Questions

4. Type of Designs

5. Observational study

7. Types of Questions Describing natural events Assessing association of observed interesting factors and outcomes Evaluating effect of assigned interesting factor on outcome 4

8. 5 Type of Designs Assignedexposure E=Exposure O=Outcome Experimental No comparison group X-sectional Descriptive longitudinal Naturalexposure Observational Cohort (Prospective ; E -> O) Analytical Case-control (Retrospective ; O -> E) With comparison group Cross-sectional (Concurrent ; E/O)

9. 1 NOVEMBER 2003 Design 1-11-03 6 “Exposures” and “Outcomes” Experimental studies - Investigator assigns exposure - Investigator assesses outcome Observational studies - Individualassigns exposure - Investigator assesses outcome

10. Results 7 Results (Data or Fact) Study procedures Questions + True value Error Randomerror (Chance) Systematicerror (Bias) Proper statistics Proper design and methodology

11. 8 BIAS Systematicdeviationfromthetruththat distortstheresultsofresearch Occur anywhere within the research process

12. 9 Interest association CONFOUNDING Outcome Exposure CA Colon Junk Food Confounder Smoking

13. 10 CONFOUNDING The distortion of the apparent effect of an exposure on risk brought about by the association with other factors that can influence the outcome e.g. effect of coffee drinking on myocardial infarction is measures as estimated relative risk of 1.8 The specific relative risk in non-smokers is 1.2 The specific relative risk in smokers is 2.7

15. 12 Study Designs No comparison group Descriptive Naturalexposure Observational

16. 13 Descriptive Study A study concerned with and designed to describe the existing distribution of interest outcomes, without regard to causal or other hypotheses

17. 14 Example of descriptive study The Epidemiological Study of Teenage Pregnancy In Malawi, during 2000-2008 DISCUSSION The Epidemiological Study of Incidence of Lung Cancer In Thailand during 2000-2005, and major Risk Factors

18. Random Sample Follow-up bias -main outcome -other interested outcomes Structure of descriptive study Population; the group to be concluded by the study results Selection bias Cross-sectional OR Longitudinal Measurement bias

21. 18 COHORT CASE - CONTROL CROSS-SECTIONAL ANALYTICAL STUDY EXPOSURE OUTCOME PRESENT FUTURE PAST

22. 19 With outcome Without outcome With outcome Without outcome Cohort Selected for study Exposed group Non-exposed group COHORT STUDY

23. Having circulatory disease No circulatory disease Having circulatory disease No circulatory disease Pregnant women with hypertensive disease Pregnant women during 1951-1970 1999 Pregnant women without hypertensive disease COHORT STUDY 20

24. 21 Retrospective COHORT STUDY DESIGNS Select groups in 2003 Trace 2028 1968 2003

25. 22 Prospective COHORT STUDY DESIGNS Select groups in 2003 Follow 2028 1968 2003

26. 23 Prospective Retrospective COHORT STUDY DESIGNS Historical prospective Select groups in 2003 Follow Follow 2028 1968 2003

28. Temporality (time-sequence)

30. Efficient for studying rare exposures

32. Loss to follow-up

35. 29 Potentialconfoundingvariablesincluding age,bodymassindex, hormonesfortreatingthemenopause, alcohol, multivitamin, andvitamin Esupplementswereupdatedeverytwoyears. Aspirinusewasassessedin 1980, 1982, 1984, and 1988. Vigorousexercisewasassessedin 1980.

36. 30 Statistical Analysis: Therelativeriskwascomputedastheratein a specificcategoryofpassive smoking dividedbythatinthelowestcategory (almostnever),withadjustmentforageinfive­yearcategories. Inmultivariateanalyses, intakeoftotalenergy, fat intake, andotherpotentialconfoundingvariableswere simultaneouslyincluded .