This document discusses different risk measures used in epidemiology, including relative risk, odds ratio, and attributable risk. Relative risk measures the strength of association between an exposure and disease based on prospective studies. Odds ratio is used similarly in case-control studies when relative risk cannot be directly calculated. Attributable risk determines how much disease can be attributed to a specific exposure by comparing disease rates in exposed and unexposed groups. These measures provide important information for evaluating disease causation and determining potential disease prevention through reducing exposures.

1. Relative and
Attributable Risks
BY
DR MUHAMMAD TAUSEEF JAVED
CONSULTANT MINISTRY OF HEALTH
MAKKAH KSA
&
IPH LAHORE

2. Absolute Risk
• Involves people who contract
disease due to an exposure
• Doesn’t consider those who are sick
but haven’t been exposed

3. Calculating Excess Risk

4. Relative Risk
Definition:
A measure of the strength of
association based on prospective
studies (cohort studies).

5. Determining Relative Risk

6. Interpreting Relative Risk

7. Relative Risk Calculations

8. Relative Risk Calculations (cont.)

9. 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

10. Odds Ratio in
Prospective (Cohort) Studies

11. Odds Ratio in
Case-Control Studies

12. Odds Ratio in
Case-Control Studies (cont.)

13. 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

14. 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

15. Attributable Risk
Definition:
The amount of disease that can be
attributed to a certain exposure.

16. Concept of Attributable Risk

17. Attributable Risk for an
Exposed Group

18. OR, expressed as a proportion:
Attributable Risk for an
Exposed Group (cont.)
From previous relative risk example:

19. 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

20. Calculations for
Attributable Risks (cont.)

21. Summary
• 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