Study designs

Study design presentation

1. STUDY DESIGNS PRESENTED BY: Dr. Parth K. Vachhani

2. introduction A study design is a specific plan or protocol for conducting the study, which allows the investigator to translate the conceptual hypothesis into an operational one. 05-Jan-15 2

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4. CONTD. Observational : Studies that do not involve any intervention or experiment. Experimental : Studies that entail manipulation of the study factor (exposure) and randomization of subjects to treatment (exposure) groups. 05-Jan-15 4

5. HIERARCHY OF STUDY DESIGN

6. OBSERVATIONAL STUDIES 05-Jan-15 6

7. Observational Studies N on-experimental O bservational because there is no individual intervention T reatment and exposures occur in a “ non-controlled ” environment I ndividuals can be observed prospectively, retrospectively or currently . 05-Jan-15 7

8. Descriptive Studies 05-Jan-15 8

9. Case Reports Detailed presentation of a single case or handful of cases Generally report a new or unique finding e.g. previous undescribed disease e.g. unexpected link between diseases e.g. unexpected new therapeutic effect e.g. adverse events 05-Jan-15 9

10. Case Series Experience of a group of patients with a similar diagnosis Cases may be identified from a single or multiple sources Generally report on new/unique condition 05-Jan-15 10

11. CONTD. Advantages Useful for hypothesis generation Informative for very rare disease with few established risk factors Disadvantages Cannot study cause and effect relationships Cannot assess disease frequency 05-Jan-15 11

12. Case Report Case Series One case of unusual findings Multiple cases of findings 05-Jan-15 12

13. Analytical Studies 05-Jan-15 13

14. Basic Question in Analytic study Are exposure and disease linked? E D Exposure Disease 05-Jan-15 14

15. Analytic study Group data Ecologic study Individual data Cross-sectional study Case-control study Cohort study 05-Jan-15 15

16. ECOLOGICAL STUDY 16 An investigation of the distribution of health and its determinants between groups of individuals . Unit of study is the aggregate data not individual level. It is usually be conducted as the first step study for research. The result is difficult to interpret because of confounding and bias. 05-Jan-15

17. CONTD. Advantages Cheap , quick and convenient since it usually come from existing data Disadvantages I nability to link exposure with disease in individual (ecological fallacy) L imit to control effect of other factors 05-Jan-15 17

18. Cross-sectional studies An “observational” design that surveys exposures and disease status at a single point of time (a cross-section of the population) time Study only exists at this point in time 05-Jan-15 18

19. CONTD. time Study only exists at this point in time Study population No Disease Disease factor present factor absent factor present factor absent 05-Jan-15 19

20. CONTD. Often used to study conditions that are relatively frequent with long duration of expression (nonfatal, chronic conditions) It measures prevalence, not incidence of disease Not suitable for studying rare or highly fatal diseases or a disease with short duration of expression 05-Jan-15 20

21. Advantages Gives general description or scope of problem Useful in health service evaluation and planning Baseline for prospective study Low-cost 05-Jan-15 21

22. DISADVANTAGES 05-Jan-15 22 No calculation of risk Temporal sequence is unclear Not good for rare diseases Selective recall can lead to bias

23. CASE CONTROL STUDY A n “observational” design comparing exposures in disease cases vs. healthy controls from same population. E xposure data collected retrospectively. M ost feasible design where disease outcomes are rare . 05-Jan-15 23

24. Case-Control Design Study population Cases (disease) Controls (no disease) factor present factor absent factor present factor absent present past time Study begins here 05-Jan-15 24

25. Odds ratio Odds ratio= ad/ bc 05-Jan-15 25 Suspected Risk Factor Cases Controls Present a b Absent c d a+c b+d

26. ADVANTAGES Cheap, easy and quick studies Require comparatively few subjects Multiple exposures can be examined Rare diseases and diseases with long latency can be studied Suitable when randomization is unethical 05-Jan-15 26

27. DISADVANTAGES Case and control selection troublesome Subject to bias Direct estimation of incidence is not possible If the incidence of exposure is high, it is difficult to show the difference between cases and controls 05-Jan-15 27

28. Cohort study A n “observational” design comparing individuals with a known risk factor or exposure with others without the risk factor or exposure. L ooking for a difference in the risk (incidence) of a disease over time. One of best observational design. D ata usually collected prospectively (some retrospective) 05-Jan-15 28

29. Cohort Design time Study begins here Study population free of disease Factor present Factor absent disease no disease disease no disease present future 05-Jan-15 29

30. 05-Jan-15 30 Disease Total Present Absent Exposure present a b a+b Exposure absent c d c+d Contd.

31. ADVANTAGES Can establish population-based incidence Accurate relative risk (risk ratio) estimation Can be used where randomization is not possible Selection and information biases are decreased Multiple outcomes can be studied 05-Jan-15 31

32. DISADVANTAGES Lengthy and expensive May require large samples Not suitable for rare diseases Not suitable for diseases with long-latency Unexpected environmental changes may influence the association Nonresponse, migration and loss-to-follow-up biases 05-Jan-15 32

33. EXPERIMENTAL STUDY 05-Jan-15 33

34. Experimental Study T reatment and exposures occur in a “ controlled ” environment P lanned research designs C linical trials are the most well known experimental design. 05-Jan-15 34

35. CONTD. I nvestigator can “control” the exposure akin to laboratory experiments except living populations are the subjects G enerally involves random assignment to groups The ultimate step in testing causal hypotheses 05-Jan-15 35

36. Randomized Controlled Trial A design with subjects randomly assigned to “treatment” and “comparison” groups. Provides most convincing evidence of relationship between exposure and effect. N ot possible to use RCTs to test effects of exposures that are expected to be harmful for ethical reasons . 05-Jan-15 36

37. Experimental Design time Study begins here (baseline point) Study population Intervention Control outcome no outcome outcome no outcome baseline future RANDOMIZATION 05-Jan-15 37

38. T he “gold standard” of research designs P rovides most convincing evidence of relationship between exposure and effect T rials of hormone replacement therapy in menopausal women found no protection for heart disease, contradicting findings of prior observational studies 05-Jan-15 38 CONTD.

39. Ability to randomize subjects Temporal sequence of cause and effect Can control extraneous variables Best evidence of causality ADVANTAGES 05-Jan-15 39

40. DISADVANTAGES 05-Jan-15 40 E xpensive It may be unethical to assign persons to certain treatment or comparison groups

41. Other Types of Experimental Study Field trials Community trials Animal studies 05-Jan-15 41

42. Meta analysis Meta-analysis is a statistical analysis of a collection of studies. Meta-analysis methods focus on contrasting and comparing results from different studies in anticipation of identifying consistent patterns and sources of disagreements among these results. 05-Jan-15 42

43. THANK YOU 05-Jan-15 43