Study design in research

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Study design in research

  1. 1. STUDY DESIGN IN RESEARCH* Few jewels from ocean Dr. Kusum Gaur Professor, PSM WHO Fellow IEC
  2. 2. Definition of Research“Research is a systematized effort to gain new knowledge”.12/08/2012 Dr. Kusum Gaur 2
  3. 3. Steps in Research (Holy 11) 1. Collect review of literature/Situation Analysis 2. Identify and prioritize health problems 3. Decide aims & objectives 4. Planning Methodology including study design 5. Execution 6. Compilation, Classification & Presentation of data 7. Analysis 8. Test of Significance/Test of Hypothesis 9. Inferences 10. Report Writing 11. Dissemination of Report12/08/2012 Dr. Kusum Gaur 3
  4. 4. Study Design 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.12/08/2012 Dr. Kusum Gaur 4
  5. 5. Direction of StudyBackward Forward Cross -sectionalRetrospective Prospective 3 4. Ambidirectional 12/08/2012 Dr. Kusum Gaur 5
  6. 6. Decision Tree Intervention Done No Yes Observational Study Experimental Study Comparison Group Randomization No Yes No YesDescriptive Study Analytic Study NRCT Study RCT Study Direction of StudyE O E OCohort Study E = O Case-Control Study Cross-Sectional Study 12/08/2012 Dr. Kusum Gaur 6
  7. 7. Epidemiological Study Design Observational Studies  Descriptive Studies Analytic Cross-Sectional Case-Control Cohort Experimental / Interventional studies As per Control: RCT/NRCT As per Blinding: Single /Double Blind As per Design: Simple/Cross-over As per Area: Field/Clinical/Lab12/08/2012 Dr. Kusum Gaur 7
  8. 8. Descriptive Studies • Case reports • Case series • Population studies12/08/2012 Dr. Kusum Gaur 8
  9. 9. Descriptive Studies: Uses • Hypothesis generating • Suggesting associations12/08/2012 Dr. Kusum Gaur 9
  10. 10. Descriptive Type of Observational Study• Other Name Case-Series/Population• Unit of Study Case/Individuals• Study Question What is happening • Direction Of Inquiry• Study Design ☻☻☻☻☻☻ desired information ☻☻☻☻☻☻ about cases/individuals is collected12/08/2012 Dr. Kusum Gaur 10
  11. 11. Case-Series …….Advantages• Easy to do• Excellent at identifying unusual situation• Good for generating hypothesesDisadvantages• Generally short-term• Investigators self-select (bias!)• no controls09/03/2010 Dr. Kusum Gaur 11
  12. 12. Analytical Observational Studies • Cross-sectional • Case-control • Cohort12/08/2012 Dr. Kusum Gaur 12
  13. 13. Cross-sectional Study • Data collected at a single point in time • Describes associations • Prevalence A “Snapshot”12/08/2012 Dr. Kusum Gaur 13
  14. 14. Cross-Sectional Study• Other Name Prevalence Study• Unit of Study Individual• Study Question What is happening • Direction of Inquiry• Study Design Exposed to Factor Not  Exposed Diseased to Factor Population Exposed to  Factor Non- Disease Not Exposed to12/08/2012 Dr. Kusum Gaur Factor 14
  15. 15. Objectives of a Cross-Sectional Study To find out association12/08/2012 Dr. Kusum Gaur 15
  16. 16. Cross-sectional Study Sample of Population Defined Population Regular Not doing meditation Meditation Prevalence of Prevalence of DM DM Time Frame = Present12/08/2012 Dr. Kusum Gaur 16
  17. 17. Cross-sectional StudyE.G. Out of 1000 population if 100 were doing meditation regularly &out of that only 2 were having DM. Remaining 900 were not doingmeditation at all, out of that 220 were having DM. + DM - 2 98 Meditation + - 220 68012/08/2012 Dr. Kusum Gaur 17
  18. 18. Cross-Sectional Study • Strengths – Quick – Cheap • Weaknesses – Cannot establish cause-effect09/03/2010 Dr. Kusum Gaur 18
  19. 19. Case-Control Studies  Start with people who have disease(Cases)  Match them with controls that do not have disease (Match Confounding)  Look back and assess exposures12/08/2012 Dr. Kusum Gaur 19
  20. 20. Controls A control is a standard of comparison (confounded with variability but without effect) for • Effects • Variability12/08/2012 Dr. Kusum Gaur 20
  21. 21. Case-Control Study• Other Name Retrospective Study• Unit of Study Cases/Control• Study Question What has happened • Direction of Inquiry= F O• Study Design Exposed  Cases Not Exposed Exposed Control Not Exposed12/08/2012 Dr. Kusum Gaur 21
  22. 22. Objective of a Case-Control Study To find out association To assess Risk Ratio12/08/2012 Dr. Kusum Gaur 22
  23. 23. Case-Control Study Cases Regular Meditation Patients with DM No Meditation Controls Regular Meditation Persons w/o DM No Meditation Past Present12/08/2012 Dr. Kusum Gaur 23
  24. 24. The logic of Case-Control StudiesCases differ from controls only in having the diseaseIf exposure does not predispose to having the disease, then exposure should be equally distributed between the cases and controls. The extent of greater previous exposure among the cases reflects the increased risk that exposure confers12/08/2012 Dr. Kusum Gaur 24
  25. 25. Case-Control Studies: Strengths• Good for rare outcomes: cancer• Can examine relation of exposures to disease• Useful to generate hypothesis• Fast• Cheap• Provides Odds Ratio 09/03/2010 Dr. Kusum Gaur 25
  26. 26. Case-Control Studies: Weaknesses • Cannot measure – Incidence – Prevalence – Relative Risk • Can only study one outcome • High susceptibility to bias09/03/2010 Dr. Kusum Gaur 26
  27. 27. Cohort Study • Begin with disease-free individuals • Classify patients as exposed/unexposed • Record outcomes in both groups • Compare outcomes using relative risk12/08/2012 Dr. Kusum Gaur 27
  28. 28. Cohort Study• Other Name Prospective Study / Follow-up Study/Incidence Study• Unit of Study Individual• Study Question What is happening • Direction of InquiryF O Diseased• Study Design• Exposed to Factor Not Non Diseased Cohort Cohort Diseased Not Exposed to Factor Non-Diseased12/08/2012 Dr. Kusum Gaur 28
  29. 29. Logic of Cohort StudyCohort is a group of persons sharing a common characteristicsDifferences in the rate at which exposed and control subjects contract a disease is due to the differences in exposure, since others are known and similar.12/08/2012 Dr. Kusum Gaur 29
  30. 30. Cohort Study Prospective (usually) Controlled Can determine causes and incidence of diseases as well as identify risk factors Generally expensive, time consuming and difficult to carry out12/08/2012 Dr. Kusum Gaur 30
  31. 31. Steps for Cohort StudyIdentify geographically defined groupIdentify exposed subjects and not exposed subjectsFollow over a specific timeRecord the fraction in each group who develop the condition of interestCompare these fractions using RR, AR or OR12/08/2012 Dr. Kusum Gaur 31
  32. 32. Objectives of a Cohort Study  To find out association To assess Risk Ratio To find out Relative Risk To find out Attributed Risk12/08/2012 Dr. Kusum Gaur 32
  33. 33. Prospective Cohort Study DMNo Meditation No DM Cohort DMRegularMeditation No DM Present Future12/08/2012 Dr. Kusum Gaur 33
  34. 34. Cohort Study: Strengths • Can measure multiple outcomes • Can adjust for confounding variables • Can calculate Attributed Risk09/03/2010 Dr. Kusum Gaur 34
  35. 35. Cohort Study: Weaknesses • Expensive • Time consuming • Cannot study rare outcomes • Confounding variables09/03/2010 Dr. Kusum Gaur 35
  36. 36. Measurements of Association Cohort Study Case Control Study •Significance Test •Significance Test •Relative Risk •OR •Attributable Risk •OR12/08/2012 Dr. Kusum Gaur 36
  37. 37. Measures of Association Significance Test – to test significance of difference in exposure between control and Cases Odds ratio - ratio of the odds of contracting disease in given exposure Relative Risk – Ratio between incidence among exposed and incidence among non-exposed Attributed Risk – percentage of difference between incidence among exposed and non-exposed with incidence among exposed RR or OR of 1 indicate no effect of exposure (equal odds)12/08/2012 Dr. Kusum Gaur 37
  38. 38. ‘Z’ Score of Exposure Rates Cases control Exposed a b a x 1ooExposure Rates = in Cases Non- c d exposed(P2) a+c b x 1ooExposure Rates = in Controls P2 – P1(P1) b+d Z Score = SEDP P1 Q 1 P 2 Q 2 SEDP = ------------- + -------- 09/03/2010 Dr. Kusum Gaur 38 N1 N2
  39. 39. ad ODD’s Ratio = Times bc Incidence among Exposed RR = Times Incidence among Non-Exposed a/a+b a (c+d) = = c/c+d c (a+b)09/03/2010 Dr. Kusum Gaur 39
  40. 40. Attributed Risk (Incidence among Exposed - Incidence among Non-Exposed) AR = x 100 Incidence among Exposed a Incidence among Exposed= x 100 a+b c Incidence among Non-Exposed= x 100 c+d09/03/2010 Dr. Kusum Gaur 40
  41. 41. Experimental Studies Clinical trials provide the “gold standard” of determining the relationship between factor and the event12/08/2012 Dr. Kusum Gaur 41
  42. 42. Types of Experimental StudyAs per Randomization: • Randomized Control Trials (RCT) • Concurrent Parallel Design (RCT) • Sequential RCT Design • RCT with External Control • Non – Randomized Trials12/08/2012 Dr. Kusum Gaur 42
  43. 43. Types of Experimental Study….As per Construction: • Simple • Cross-Over Study DesignAs per Study Area: • Field Trials • Clinical Trials • Lab. Trials 12/08/2012 Dr. Kusum Gaur 43
  44. 44. Quality of Experimental Study • Randomization • Blinding • Control • Cross-Over12/08/2012 Dr. Kusum Gaur 44
  45. 45. Controls in Clinical Trials A clinical trial is a comparative, prospective experiment conducted in human subjects• Historical controls are better than no controls• Patients can serve as own controls - This is usually beneficial as the comparison removes patient differences12/08/2012 Dr. Kusum Gaur 45
  46. 46. Blinding Good practice: factors that can affect the evaluation of outcome should not be permitted to influence the evaluation process Single-blind Patient or evaluator (either of one) is blinded as to intervention Double-blind design Neither patient nor outcome evaluator knows Rx to which patient was assigned12/08/2012 Dr. Kusum Gaur 46
  47. 47. Randomized Control Trials (RCT)• Before and After Comparison• Comparison with Placebo• Comparison Of two medicine/procedure/tests• Comparison Of > two medicine/procedure/tests12/08/2012 Dr. Kusum Gaur 47
  48. 48. Experimental Study• Other Name Intervention Study• Objective To know the effect of intervention• Unit of Study Individual meeting entry criteria• Study Question What is happening after intervention in both groups • Direction of Inquiry I E• Study Design 1(Intervention with Placebo) Positive Outcome Group 1/cases Intervention Negative Outcome Positive Outcome Group Placebo 2/control Negative Outcome12/08/2012 Dr. Kusum Gaur 48
  49. 49. Clinical Trial R Treatment a Outcomes Group n d Study o Population m i z Outcomes e Control Group12/08/2012 Dr. Kusum Gaur 49
  50. 50. Intervention Study - Design 2 (Comparison of Effect of Two Interventions) Cases Meeting Entry criteria Group - 1 Group -2 Intervention -1 Intervention Intervention - 2 Positive Negative Positive Outcome Negative Outcome Outcome Outcome12/08/2012 Dr. Kusum Gaur 50
  51. 51. Cross Over Design Group -1 Cases Group-2 Meeting Entry criteria Intervention - 2 Intervention - 1 Positive Negative Positive Negative Outcome Outcome Outcome Outcome Group -1 Group -2 Crossover Intervention -2 Intervention -1 Positive NegativePositive Negative Outcome Outcome OutcomeOutcome 12/08/2012 Dr. Kusum Gaur 51
  52. 52. Other Types of Experimental Study • Quincy Experimental Study • Block Experimental Study12/08/2012 Dr. Kusum Gaur 52
  53. 53. Quincy Experimental Study Cases Meeting Entry criteria Group - 1 Group -2 Intervention Intervention No Intervention Positive Negative Positive Outcome Negative Outcome Outcome Outcome12/08/2012 Dr. Kusum Gaur 53
  54. 54. Block Experimental Study Cases Meeting Entry criteria Group -3 Group - 1 Group -2 Intervention Intervention-3 Intervention -1 Intervention Intervention-2Positive Positive Negative NegativeOutcome Outcome Outcome Outcome Positive Negative Outcome Outcome 12/08/2012 Dr. Kusum Gaur 54
  55. 55. Steps of Experimental Study Drawing up a Protocol Reference Population Sample Population Exclusions Randomization Experimental Group Control Group Manipulation/Intervention Follow - up12/08/2012 Assessment of Outcome Dr. Kusum Gaur 55
  56. 56. Ideal Study Design for established causality Ethical Issues
  57. 57. STUDY QUESTIONS AND APPROPRIATE DESIGNS Type of Question Appropriate Study Design Burden of illness Field Surveys - Prevalence Cross Sectional Survey - Incidence Longitudinal survey Causation, Risk & Prognosis Case Control Study, Cohort study, RCT Treatment Efficacy Randomized Controlled study Diagnostic Test Evaluation Randomized Controlled study Cost Effectiveness Randomized Controlled study12/08/2012 Dr. Kusum Gaur 57
  58. 58. Hierarchy of Epidemiological Study Design Establish Causality RCT Cohort Case Control Cross-Sectional Case SeriesGenerate Hypothesis Case Report12/08/2012 Dr. Kusum Gaur 58
  59. 59. 12/08/2012 Dr. Kusum Gaur 59

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