A Brief Introduction to Epidemiology XI Epidemiologic Research Designs: ExperimentalInterventional S

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A Brief Introduction to Epidemiology -
XI(Epidemiologic Research DesignsExperimental/I
nterventional 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 studys degree of internal validity depends on
  the study designs 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
New Treatment
R A N D O M I Z E D
Not Improved
Defined Population
Improved
Current Treatment
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/