A Brief Introduction to Epidemiology - XI (Epidemiologic Research

							              A Brief Introduction to
                Epidemiology - XI
           (Epidemiologic Research Designs:
          Experimental/Interventional Studies)

              Betty C. Jung, RN, MPH, CHES


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   Learning Objectives
          To   understand:
           – What experimental studies are
           – The value of such studies
           – The basic methodology
           – Pros and Cons of such studies




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   Introduction
          The primary purpose of research is to
           conduct a scientific, or, scholarly
           investigation into a phenomenon, or
           to answer a burning question.
          Research is defined as a systematic
           approach to problem solving.


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   Epidemiological Study Designs
           Observational    Studies - examine
            associations between risk factors and
            outcomes (Analytical - determinants and
            risk of disease, and descriptive - patterns
            and frequency of disease)
           Intervention Studies - explore the
            association between interventions and
            outcomes. (Experimental studies or
            clinical trials)
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   Epidemiological Study Designs
         Observational
          – Cross-Sectional
          – Case-control
          – Cohort
  Interventional
          – Natural Experiment (Community Trial)
          – Field Trial
          – Experiment/Randomized Trails (ex. Clinical Trial)
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   Examples of Experimental
   Epidemiologic Studies
     Prophylactic    vaccines tested on children
      populations to prove the efficacy of the
      vaccines in preventing the diseases (i.e., polio)
     Prophylaxis with drugs in preventing disease
      (i.e., penicillin to prevent rheumatic fever)
     Impact on health-related behavior and
      coronary heart disease in response to
      community-wide heart disease prevention
      intervention
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   Value
     Experiments   are seen as the “Supreme Court” of
      epidemiologic research as they provide the
      strongest possible evidence of disease causation.
     Experimental study designs can rule out with
      greater certainty factors that may confound
      potential cause and affect relationships.
     A study’s degree of internal validity depends on
      the study design’s ability to determine whether
      an antecedent causes an effect (or outcome).
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   Community Trials

          Communities    rather than individuals
           comprise the treatment groups
          Appropriate for diseases that have their
           origins in social conditions that can be
           influenced by intervention directed at
           group behavior as well as individuals


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          Limitations of Community Trials
     Random   allocation of communities is
      not practical
     Only a small number of communities
      can be included
     Other methods are needed to ensure any
      difference found can be attributed to the
      intervention rather than to any inherent
      differences between the communities
      studied
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   Field Trials
          Involve  people who are disease-free
           but presumed to be at risk
          Data collection – “in the field” –
           among non-institutionalized people
           in the general population
          Used to evaluate interventions that
           reduce exposure without measuring
           the occurrence of health effects.

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   Limitations of Field Trials
          Hugh  undertaking
          Major logistic considerations
          Major financial considerations
          Think of how much work is required
           to randomize and allocate
           participants to various treatment
           groups!

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   Experimental Study Design
          Time                Treated - Improved
               Treated (T)
                              Treated – Not Improved
Sample of
  Cases
                              Not Treated - Improved
           Not Treated (NT)
               (Control)      Not Treated – Not Improved


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   Randomized Trial Methodology

           Random   allocation - Each subject has an
            equal chance of being assigned to any
            group in the study, so that all groups in a
            study are similar in all characteristics not
            controlled by other methods, such as
            subject selection.
           Random allocation can be used with
            matching to ensure the study groups are
            comparable
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   Randomized Trial Design
          Time
                               Improved
           R       New
           A
           N
                 Treatment
 Defined   D
                             Not Improved
Population O
           M
           I                  Improved
           Z
                  Current
           E     Treatment
           D                 Not Improved

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     Four Possibilities
          The treatments do not differ and we
           correctly conclude they do not differ
          The treatments do not differ but we
           conclude they do differ
          The treatments differ but we conclude
           they do not differ
          The treatments do differ and we
           correctly conclude that they do differ
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   Pros
           Helpful in assessing the value of new
            therapies to combat acute diseases in
            developing countries
           Can evaluate a single variable in a precisely
            defined patient group
           Prospective design
           Eliminates bias by comparing two otherwise
            identical groups
           Allows for meta-analysis
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   Cons
           Expensive   and time consuming
           Not always properly conducted – too few
            subjects, too short a time period
           Influence of sponsorship
           Use of surrogate endpoints may
            introduce “hidden bias”
           Failure to randomize all eligible subjects
           Failure to blind assessors to randomized
            status of subjects
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   References
          For  Internet Resources on the
           topics covered in this lecture,
           check out my Web site:
              http://www.bettycjung.net/




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