relative and atribute risk
TRANSCRIPT
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Relative and Attributable Risks
BY DR MUHAMMAD TAUSEEF JAVED
CONSULTANT MINISTRY OF HEALTH MAKKAH KSA
&IPH LAHORE
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Absolute Risk
• Involves people who contract disease due to an exposure
• Doesn’t consider those who are sick but haven’t been exposed
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Calculating Excess Risk
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Relative Risk
Definition:
A measure of the strength of association based on prospective studies (cohort studies).
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Determining Relative Risk
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Interpreting Relative Risk
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Relative Risk Calculations
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Relative Risk Calculations (cont.)
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Relative Risk in Case-Control Studies
• Can’t derive incidence from case-control studiesBegin 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
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Odds Ratio in Prospective (Cohort) Studies
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Odds Ratio in Case-Control Studies
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Odds Ratio in Case-Control Studies (cont.)
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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
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REMEMBER !!!
• An odds ratio is a useful measure of association
• 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
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Attributable Risk
Definition:
The amount of disease that can be attributed to a certain exposure.
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Concept of Attributable Risk
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Attributable Risk for an Exposed Group
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OR, expressed as a proportion:
Attributable Risk for an Exposed Group (cont.)
From previous relative risk example:
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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
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Calculations for Attributable Risks (cont.)
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Summary• Relative risk and odds ratio are important as
measures of the strength of associationImportant for deriving causal inference
• Attributable risk is a measure of how much disease risk is attributed to a certain exposureUseful 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