Lec13AttributableRelativeRisks_Revised07_ by gulferoz


									   Relative and
Attributable Risks
         Absolute Risk
• Involves people who contract
  disease due to an exposure
• Doesn’t consider those who are sick
  but haven’t been exposed
Calculating Excess Risk
       Relative Risk

     A measure of the strength of
association based on prospective
studies (cohort studies).
Determining Relative Risk
Interpreting Relative Risk
Relative Risk Calculations
Relative Risk Calculations (cont.)
       Relative Risk in
     Case-Control Studies
• Can’t derive incidence from case-
  control studies
  Begin with diseased people (cases) and
   non-diseased people (controls)
• Therefore, can’t calculate relative
  risk directly
• But, we can use another method
  called an odds ratio
      Odds Ratio in
Prospective (Cohort) Studies
   Odds Ratio in
Case-Control Studies
     Odds Ratio in
Case-Control Studies (cont.)
When is the Odds Ratio a Good
 Estimate of Relative Risk?

 • When cases are representative of
   diseased population
 • When controls are representative of
   population without disease
 • When the disease being studied
   occurs at low frequency
         REMEMBER !!!
• An odds ratio is a useful measure of
• In a cohort study, the relative risk
  can be calculated directly
• In a case-control study the relative
  risk cannot be calculated directly, so
  an odds ratio is used instead
        Attributable Risk

      The amount of disease that can be
attributed to a certain exposure.
Concept of Attributable Risk
Attributable Risk for an
    Exposed Group
Attributable Risk for an
 Exposed Group (cont.)
     From previous relative risk example:

   OR, expressed as a proportion:
 Calculation for Proportional
Incidence in Total Population
First calculate A-R for
      group from
 Formulas 11.1 & 11.2
   (previous slide),
then use Formula 11.3

For proportion of the
   incidence in the
total population, use
     Formula 11.4
    Calculations for
Attributable Risks (cont.)
• Relative risk and odds ratio are important as
  measures of the strength of association
   Important for deriving causal inference
• Attributable risk is a measure of how much
  disease risk is attributed to a certain exposure
   Useful in determining how much disease can
    be prevented
• Therefore:
   Relative risk is valuable in etiologic studies
    of disease
   Attributable risk is useful for Public Health
    guidelines and planning

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