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STUDY DESIGN
                    IN
                 RESEARCH




*   Few jewels from ocean
                            Dr. Kusum Gaur
                            Professor, PSM
                            WHO Fellow IEC
Definition of Research

“Research is a
       systematized effort
                to gain new knowledge”.




12/08/2012      Dr. Kusum Gaur        2
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 Report


12/08/2012               Dr. Kusum Gaur                  3
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
Direction of Study

Backward                                      Forward


                Cross -sectional

Retrospective                                 Prospective
                                          3



                4. Ambidirectional
 12/08/2012              Dr. Kusum Gaur                     5
Decision Tree
                                Intervention Done
                     No                                            Yes
               Observational Study                           Experimental Study

               Comparison Group                                Randomization

       No                      Yes
                                                           No                Yes
Descriptive Study        Analytic Study
                                                         NRCT Study        RCT Study

                        Direction of Study


E   O                                                           E    O
Cohort Study              E = O                       Case-Control Study
                     Cross-Sectional Study


  12/08/2012                         Dr. Kusum Gaur                               6
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/Lab
12/08/2012              Dr. Kusum Gaur     7
Descriptive Studies


             • Case reports
             • Case series
             • Population studies



12/08/2012                    Dr. Kusum Gaur   8
Descriptive Studies: Uses


      • Hypothesis generating


      • Suggesting associations



12/08/2012          Dr. Kusum Gaur   9
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 collected


12/08/2012              Dr. Kusum Gaur                10
Case-Series …….
Advantages
• Easy to do
• Excellent at identifying unusual situation
• Good for generating hypotheses

Disadvantages
• Generally short-term
• Investigators self-select (bias!)
• no controls

09/03/2010              Dr. Kusum Gaur         11
Analytical Observational Studies


             • Cross-sectional

             • Case-control

             • Cohort



12/08/2012         Dr. Kusum Gaur   12
Cross-sectional Study
   • Data collected at a single point in time



   • Describes associations



   • Prevalence
                         A “Snapshot”

12/08/2012               Dr. Kusum Gaur         13
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 to
12/08/2012                      Dr. Kusum Gaur   Factor       14
Objectives of a Cross-Sectional Study



             To find out association




12/08/2012            Dr. Kusum Gaur   15
Cross-sectional Study

                      Sample of Population
                      Defined Population

              Regular                  Not doing meditation
              Meditation


              Prevalence of                    Prevalence of
                   DM                               DM



                       Time Frame = Present
12/08/2012                    Dr. Kusum Gaur                   16
Cross-sectional Study
E.G. Out of 1000 population if 100 were doing meditation regularly &
out of that only 2 were having DM. Remaining 900 were not doing
meditation at all, out of that 220 were having DM.

                         +     DM                -

                       2                         98
      Meditation




                   +



                   -   220                       680


12/08/2012                      Dr. Kusum Gaur                         17
Cross-Sectional Study

   • Strengths
         – Quick
         – Cheap

   • Weaknesses
         – Cannot establish cause-effect


09/03/2010               Dr. Kusum Gaur    18
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 exposures

12/08/2012           Dr. Kusum Gaur            19
Controls

  A control is a standard of comparison
   (confounded with variability but without
   effect)
      for

                • Effects

                      • Variability
12/08/2012           Dr. Kusum Gaur           20
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
                     Exposed
12/08/2012                 Dr. Kusum Gaur             21
Objective of a Case-Control Study


             To find out association

             To assess Risk Ratio




12/08/2012             Dr. Kusum Gaur   22
Case-Control Study

                                              Cases
   Regular Meditation
                                         Patients with DM
        No Meditation


                                             Controls
 Regular Meditation
                                         Persons w/o DM
        No Meditation


             Past                          Present
12/08/2012              Dr. Kusum Gaur                      23
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 confers

12/08/2012            Dr. Kusum Gaur             24
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
Case-Control Studies: Weaknesses


     • Cannot measure
             – Incidence
             – Prevalence
             – Relative Risk
     • Can only study one outcome
     • High susceptibility to bias

09/03/2010                     Dr. Kusum Gaur   26
Cohort Study

   • Begin with disease-free individuals

   • Classify patients as exposed/unexposed

   • Record outcomes in both groups

   • Compare outcomes using relative risk


12/08/2012            Dr. Kusum Gaur          27
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-Diseased

12/08/2012                        Dr. Kusum Gaur                     28
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
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 out
12/08/2012                Dr. Kusum Gaur              30
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 OR


12/08/2012         Dr. Kusum Gaur             31
Objectives of a Cohort Study

          To find out association

         To assess Risk Ratio

         To find out Relative Risk

         To find out Attributed Risk




12/08/2012               Dr. Kusum Gaur   32
Prospective Cohort Study
                                   DM
No Meditation
                                 No DM

     Cohort
                                   DM
Regular
Meditation                       No DM

    Present                      Future
12/08/2012      Dr. Kusum Gaur            33
Cohort Study: Strengths

   • Can measure multiple outcomes

   • Can adjust for confounding variables

   • Can calculate Attributed Risk




09/03/2010            Dr. Kusum Gaur        34
Cohort Study: Weaknesses

    • Expensive

    • Time consuming

    • Cannot study rare outcomes

    • Confounding variables



09/03/2010             Dr. Kusum Gaur   35
Measurements of Association


    Cohort Study                    Case Control Study


  •Significance Test                    •Significance Test
  •Relative Risk                        •OR
  •Attributable Risk
  •OR


12/08/2012             Dr. Kusum Gaur                        36
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
‘Z’ Score of Exposure Rates

                                                               Cases            control


                                                 Exposed       a                b
                   a x 1oo
Exposure Rates =             in Cases            Non-          c                d
                                                 exposed
(P2)                 a+c

                     b x 1oo
Exposure 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
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
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+d

09/03/2010                     Dr. Kusum Gaur                                40
Experimental Studies


    Clinical trials provide the “gold standard” of

    determining    the       relationship   between

    factor and the event




12/08/2012               Dr. Kusum Gaur               41
Types of Experimental Study

As per Randomization:
      • Randomized Control Trials (RCT)
             • Concurrent Parallel Design (RCT)

             • Sequential RCT Design

             • RCT with External Control



      • Non – Randomized Trials

12/08/2012                    Dr. Kusum Gaur      42
Types of Experimental Study….

As per Construction:
                • Simple

                • Cross-Over Study Design


As per Study Area:
              • Field Trials

              • Clinical Trials

              • Lab. Trials
 12/08/2012                    Dr. Kusum Gaur   43
Quality of Experimental Study


       • Randomization

       • Blinding

       • Control

       • Cross-Over

12/08/2012               Dr. Kusum Gaur   44
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 differences
12/08/2012              Dr. Kusum Gaur               45
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 assigned

12/08/2012             Dr. Kusum Gaur              46
Randomized Control Trials
             (RCT)
• Before and After Comparison

• Comparison with Placebo

• Comparison Of two medicine/procedure/tests

• Comparison Of > two medicine/procedure/tests


12/08/2012         Dr. Kusum Gaur          47
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
                                                         Outcome

12/08/2012                        Dr. Kusum Gaur                        48
Clinical Trial


               R          Treatment
               a                       Outcomes
                            Group
               n
               d
    Study      o
  Population   m

               i
               z                       Outcomes
               e       Control Group




12/08/2012          Dr. Kusum Gaur                49
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                   Outcome




12/08/2012                                   Dr. Kusum Gaur                                     50
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                  Negative
Positive                    Negative
                                                                Outcome
                            Outcome                                                       Outcome
Outcome

  12/08/2012                                   Dr. Kusum Gaur                                        51
Other Types of Experimental Study


       • Quincy Experimental Study


       • Block Experimental Study




12/08/2012             Dr. Kusum Gaur   52
Quincy Experimental Study

                                     Cases
                                     Meeting
                                     Entry criteria

              Group - 1                                             Group -2




              Intervention                Intervention               No Intervention




   Positive               Negative                       Positive
                          Outcome                                                Negative
   Outcome                                               Outcome                 Outcome




12/08/2012                                 Dr. Kusum Gaur                                   53
Block Experimental Study

                                    Cases
                                    Meeting
                                    Entry criteria

                                                                                Group -3
           Group - 1

                                          Group -2



                                                          Intervention           Intervention-3
         Intervention -1        Intervention

                                           Intervention-2

Positive                                                             Positive                Negative
                    Negative
Outcome             Outcome                                          Outcome                 Outcome
                               Positive                   Negative
                               Outcome                    Outcome


  12/08/2012                                   Dr. Kusum Gaur                                           54
Steps of Experimental Study
                       Drawing up a Protocol


                       Reference Population


                         Sample Population


                             Exclusions


                           Randomization
             Experimental Group      Control Group


                       Manipulation/Intervention

                              Follow - up


12/08/2012              Assessment of Outcome
                         Dr. Kusum Gaur              55
Ideal Study Design for established causality




 Ethical Issues
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 study

12/08/2012                       Dr. Kusum Gaur                          57
Hierarchy of Epidemiological Study Design

  Establish Causality                         RCT

                                              Cohort

                                              Case Control


                                              Cross-Sectional

                                              Case Series


Generate Hypothesis                           Case Report

12/08/2012                   Dr. Kusum Gaur                     58
12/08/2012   Dr. Kusum Gaur   59

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Study design in research

  • 1. STUDY DESIGN IN RESEARCH * Few jewels from ocean Dr. Kusum Gaur Professor, PSM WHO Fellow IEC
  • 2. Definition of Research “Research is a systematized effort to gain new knowledge”. 12/08/2012 Dr. Kusum Gaur 2
  • 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 Report 12/08/2012 Dr. Kusum Gaur 3
  • 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. Direction of Study Backward Forward Cross -sectional Retrospective Prospective 3 4. Ambidirectional 12/08/2012 Dr. Kusum Gaur 5
  • 6. Decision Tree Intervention Done No Yes Observational Study Experimental Study Comparison Group Randomization No Yes No Yes Descriptive Study Analytic Study NRCT Study RCT Study Direction of Study E O E O Cohort Study E = O Case-Control Study Cross-Sectional Study 12/08/2012 Dr. Kusum Gaur 6
  • 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/Lab 12/08/2012 Dr. Kusum Gaur 7
  • 8. Descriptive Studies • Case reports • Case series • Population studies 12/08/2012 Dr. Kusum Gaur 8
  • 9. Descriptive Studies: Uses • Hypothesis generating • Suggesting associations 12/08/2012 Dr. Kusum Gaur 9
  • 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 collected 12/08/2012 Dr. Kusum Gaur 10
  • 11. Case-Series ……. Advantages • Easy to do • Excellent at identifying unusual situation • Good for generating hypotheses Disadvantages • Generally short-term • Investigators self-select (bias!) • no controls 09/03/2010 Dr. Kusum Gaur 11
  • 12. Analytical Observational Studies • Cross-sectional • Case-control • Cohort 12/08/2012 Dr. Kusum Gaur 12
  • 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. 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 to 12/08/2012 Dr. Kusum Gaur Factor 14
  • 15. Objectives of a Cross-Sectional Study To find out association 12/08/2012 Dr. Kusum Gaur 15
  • 16. Cross-sectional Study Sample of Population Defined Population Regular Not doing meditation Meditation Prevalence of Prevalence of DM DM Time Frame = Present 12/08/2012 Dr. Kusum Gaur 16
  • 17. Cross-sectional Study E.G. Out of 1000 population if 100 were doing meditation regularly & out of that only 2 were having DM. Remaining 900 were not doing meditation at all, out of that 220 were having DM. + DM - 2 98 Meditation + - 220 680 12/08/2012 Dr. Kusum Gaur 17
  • 18. Cross-Sectional Study • Strengths – Quick – Cheap • Weaknesses – Cannot establish cause-effect 09/03/2010 Dr. Kusum Gaur 18
  • 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 exposures 12/08/2012 Dr. Kusum Gaur 19
  • 20. Controls A control is a standard of comparison (confounded with variability but without effect) for • Effects • Variability 12/08/2012 Dr. Kusum Gaur 20
  • 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 Exposed 12/08/2012 Dr. Kusum Gaur 21
  • 22. Objective of a Case-Control Study To find out association To assess Risk Ratio 12/08/2012 Dr. Kusum Gaur 22
  • 23. Case-Control Study Cases Regular Meditation Patients with DM No Meditation Controls Regular Meditation Persons w/o DM No Meditation Past Present 12/08/2012 Dr. Kusum Gaur 23
  • 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 confers 12/08/2012 Dr. Kusum Gaur 24
  • 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. Case-Control Studies: Weaknesses • Cannot measure – Incidence – Prevalence – Relative Risk • Can only study one outcome • High susceptibility to bias 09/03/2010 Dr. Kusum Gaur 26
  • 27. Cohort Study • Begin with disease-free individuals • Classify patients as exposed/unexposed • Record outcomes in both groups • Compare outcomes using relative risk 12/08/2012 Dr. Kusum Gaur 27
  • 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-Diseased 12/08/2012 Dr. Kusum Gaur 28
  • 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. 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 out 12/08/2012 Dr. Kusum Gaur 30
  • 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 OR 12/08/2012 Dr. Kusum Gaur 31
  • 32. Objectives of a Cohort Study  To find out association To assess Risk Ratio To find out Relative Risk To find out Attributed Risk 12/08/2012 Dr. Kusum Gaur 32
  • 33. Prospective Cohort Study DM No Meditation No DM Cohort DM Regular Meditation No DM Present Future 12/08/2012 Dr. Kusum Gaur 33
  • 34. Cohort Study: Strengths • Can measure multiple outcomes • Can adjust for confounding variables • Can calculate Attributed Risk 09/03/2010 Dr. Kusum Gaur 34
  • 35. Cohort Study: Weaknesses • Expensive • Time consuming • Cannot study rare outcomes • Confounding variables 09/03/2010 Dr. Kusum Gaur 35
  • 36. Measurements of Association Cohort Study Case Control Study •Significance Test •Significance Test •Relative Risk •OR •Attributable Risk •OR 12/08/2012 Dr. Kusum Gaur 36
  • 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. ‘Z’ Score of Exposure Rates Cases control Exposed a b a x 1oo Exposure Rates = in Cases Non- c d exposed (P2) a+c b x 1oo Exposure 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. 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. 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+d 09/03/2010 Dr. Kusum Gaur 40
  • 41. Experimental Studies Clinical trials provide the “gold standard” of determining the relationship between factor and the event 12/08/2012 Dr. Kusum Gaur 41
  • 42. Types of Experimental Study As per Randomization: • Randomized Control Trials (RCT) • Concurrent Parallel Design (RCT) • Sequential RCT Design • RCT with External Control • Non – Randomized Trials 12/08/2012 Dr. Kusum Gaur 42
  • 43. Types of Experimental Study…. As per Construction: • Simple • Cross-Over Study Design As per Study Area: • Field Trials • Clinical Trials • Lab. Trials 12/08/2012 Dr. Kusum Gaur 43
  • 44. Quality of Experimental Study • Randomization • Blinding • Control • Cross-Over 12/08/2012 Dr. Kusum Gaur 44
  • 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 differences 12/08/2012 Dr. Kusum Gaur 45
  • 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 assigned 12/08/2012 Dr. Kusum Gaur 46
  • 47. Randomized Control Trials (RCT) • Before and After Comparison • Comparison with Placebo • Comparison Of two medicine/procedure/tests • Comparison Of > two medicine/procedure/tests 12/08/2012 Dr. Kusum Gaur 47
  • 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 Outcome 12/08/2012 Dr. Kusum Gaur 48
  • 49. Clinical Trial R Treatment a Outcomes Group n d Study o Population m i z Outcomes e Control Group 12/08/2012 Dr. Kusum Gaur 49
  • 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 Outcome 12/08/2012 Dr. Kusum Gaur 50
  • 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 Negative Positive Negative Outcome Outcome Outcome Outcome 12/08/2012 Dr. Kusum Gaur 51
  • 52. Other Types of Experimental Study • Quincy Experimental Study • Block Experimental Study 12/08/2012 Dr. Kusum Gaur 52
  • 53. Quincy Experimental Study Cases Meeting Entry criteria Group - 1 Group -2 Intervention Intervention No Intervention Positive Negative Positive Outcome Negative Outcome Outcome Outcome 12/08/2012 Dr. Kusum Gaur 53
  • 54. Block Experimental Study Cases Meeting Entry criteria Group -3 Group - 1 Group -2 Intervention Intervention-3 Intervention -1 Intervention Intervention-2 Positive Positive Negative Negative Outcome Outcome Outcome Outcome Positive Negative Outcome Outcome 12/08/2012 Dr. Kusum Gaur 54
  • 55. Steps of Experimental Study Drawing up a Protocol Reference Population Sample Population Exclusions Randomization Experimental Group Control Group Manipulation/Intervention Follow - up 12/08/2012 Assessment of Outcome Dr. Kusum Gaur 55
  • 56. Ideal Study Design for established causality Ethical Issues
  • 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 study 12/08/2012 Dr. Kusum Gaur 57
  • 58. Hierarchy of Epidemiological Study Design Establish Causality RCT Cohort Case Control Cross-Sectional Case Series Generate Hypothesis Case Report 12/08/2012 Dr. Kusum Gaur 58
  • 59. 12/08/2012 Dr. Kusum Gaur 59