Relative and Attributable Risks Absolute Risk Involves people

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 Definition: 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 casecontrol studies üBegin 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 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

Attributable Risk Definition: 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. )

Summary • Relative risk and odds ratio are important as measures of the strength of association üImportant for deriving causal inference • Attributable risk is a measure of how much disease risk is attributed to a certain exposure üUseful in determining how much disease can be prevented • Therefore: üRelative risk is valuable in etiologic studies of disease üAttributable risk is useful for Public Health guidelines and planning