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1. By: Ismael. A (PHD fellow in Epidemiology)

2. Session Learning Outcomes Define research designs Describe types quantitative research design. Identify advantages and limitation of each design Discuss different types of experimental and nonexperimental research designs. Define best level of evidence in each design. Describe the characteristics of quantitative research design.

3. What you understand from picture?

4. Study designs… A study design is the process that guides researchers on how to; Collect analyze and interpret observations. It is a logical model that guides the investigator in the various stages of the research Its blueprin t for the collection, measurement, and analysis of data

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7. Observational Researcher just observes and analyses researchable objects or situations but does not intervene .

8. D escriptive studies: Describe the patterns of disease occurrence and other health-related conditions by person, place and time . Personal variables : age, sex marital status or occupation, as well as the consumption of various types of food or medication use. Place : geographic distribution of disease, variation among countries or within countries(urban and rural areas). Time: examine seasonal patterns in disease onset, etc. Quantitative study design …

9. Ecological design 10 Also known as correlational study Population level measurement is made for health outcomes in relation to some factors of interest Exposure, and or health outcome data are collected at a group level. Not an individual level Generally ecologic studies use a group level of measurement

10. Example: S tudy air pollution and its health outcome . Average air pollution level would be measured at city level and death from chronic lung disease in the same city 11

11. Advantage Ecologic studies have lower cost and are convenient Data can be publicly available(registry, Census) Ecologic studies are useful for evaluating the impact of community level interventions Fluoridation of water Ecologic study is that this study design can maximize exposure differences where minimal within community differences render individual risk studies impractical Generate hypothesis 13

12. Case report and case seri e s Case Report/case study Its a careful, detailed report of the profile of a single patient Document unusual medical occurrence Can represent the first clues in the identification of new diseases . 14

13. Case series The individual case report can be expanded to a case series, which describes characteristics of a number of patients with a given disease. A series of cases - treated or untreated Describing signs, symptoms or Patho-physiological parameters in the series of patients Can lead to generating hypothesis. Case report and case seri e s …

14. Case report and case seri e s …

15. Cross-sectional study design 17 Alternative terminologies: - Survey research - Prevalence study - Survey - Sample survey (partial enumeration) In this study, a sample of persons from a population is enrolled and their exposures and health outcomes are measured simultaneously . Census and sample survey: - Census implies enumeration of entire population - Surveys examine a sample of a population

16. 19 CROSS-SECTIONAL STUDIES... Factors dictating sample surveys: - Population being large or dispersed - Shortage of financial resources - Limited time- results demanded urgently - Shortage of trained manpower - Consideration for a small population: - School children - Workers in a small factory - Inhabitants of a village 3/13/2025

17. 20 CROSS-SECTIONAL STUDIES... Surveys examine certain characteristic and proceed as follows: Consider a sample Construct a questionnaire to elicit information Administer questionnaire to a sample of study subjects: - Face-to-face interviews - Self administered formats - Mailed questionnaires 3/13/2025

18. Advantage Multiple outcomes and exposures can be studied important in public health for assessing the burden of disease in a specified population and in planning and allocating health resources Good for descriptive analyses and for generating hypotheses Inexpensive and less ti me consuming Monitor change over time 21

19. Limitation “ Chicken or egg dilemma ” or temporal ambiguity or antecedent-consequent bias effects Since exposure and outcome are measured simultaneously it is not possible to determine causal relationship Length biased sampling Disease with long duration are oversampled while disease with short duration are less represented Not suitable for rare disease or disease with short duration 22

20. Note For factors that remain unaltered over time, such as sex, blood group, etc., the cross-sectional survey can provide evidence of a valid statistical association. In general, measure prevalence rather than incidence

21. Case-control study Hierarchy of observational analytical designs validity 25 Cohort Case-control Cross-sectional Lowest Highest

22. Case-control Group of subjects with the disease- cases group of subjects without the disease- controls . Examine the association between disease and potential risk factors Concerned with identifying potential risk factors of a disease Information about previous exposures are obtained for cases and controls, and frequency of exposure compared for the two groups. 26

23. Case-control study… Epidemiological studies are carried to answer different question Cohort Study Case-control

24. Case-control study… 28 Present Past

25. Case-control study The first most important step is selection of cases and controls Precise diagnostic criteria and definition of cases Clinical, laboratory, or other criteria It is important to produce as much homogeneous disease entity as possible. Once clear diagnostic criteria and definition has been established, cases will be selected from the sources. 30

26. Case-control study… Selection of controls Controls should be Population at risk and representatives of the source population Comparable to the cases Sources of controls General populations Hospital Special (i.e. friends, neighbors, relatives) Proxy control 31

27. Ratio of control to cases When larger cases are available, the cost and difficulty of finding the controls and cases are similar and controls represent study base. Maximum statistical efficiency can be obtained with 1:1 ratio If the above conditions are not meet Up to a maximum of 4:1 ration can be considered Beyond 4:1 ratio results negligeable statistical power 32 Case-control study…

28. Information on exposure status Exposure should be clearly defined -defined when to say exposed. An appropriate time window should be considered. Consider history, duration and intensity of exposure Information about exposure Study subjects, surrogate or records The manner used to obtain information must be similar for cases and controls for comparable accuracy. 33 Case-control study…

29. Unmatched case-control vs. Matched case-control E.g. if the potential confounder is sex Selecting male control of each male cases and female control for each female cases 34 Case-control study…

30. Cohort study Is a follow up study In this study Groups of individuals are selected on the basis of exposure to suspected risk factors. The groups must bee free of the disease. Researchers F ollowed POPN at-risk over a period to assess the occurrence of the disease Determine the subsequent risk or rate of disease or health outcome.

31. Study start Study End 37 Cohort study …

32. Closed populations A closed population adds no new members over time and loses members only to death/risk free They begin with a certain number of individuals and shrink over time Cohort study …

33. Open population May gain members over time Through immigration or birth May lose members over time Through emigration or death An open population that is in a steady state is said to be stationary Over time, open populations may grow, remain the same size, or shrink . Cohort study …

34. Approaches to Follow-up 40 In cohort study we trace all participants to determine weather they develop the outcome – A failure to do this is a significant source of bias Three important concepts are Event Censored Lost to follow up Loss to follow up Affect the validity and limit the power of the study Serious if Related to exposure, outcome or both If the proportion is larger in one group

35. Limitation 41 Time consuming Expensive Prone to bias associated with loss to follow up and ascertainment of exposure

36. Summary

37. The End!! 43