Measures of Association

Question 1

What is ‘Relative Risk’?

Answer 1

Relative risks are ratios of frequency of outcome in exposed to non-exposed individuals
Relative risk of outcome - prevalence ratio, odds ratio of outcome, risk ratio, incidence rate ratio
- Odds Ratio of Exposure***

RR > 1 - Increased risk for the exposed
RR = 1 - Same level of risk for exposed and unexposed
RR < 1 = Lower risk for the exposed (protective factor)

The further RR is away from 1 the stronger the association

Question 2

What is ‘Prevalence Ratio’

Answer 2

Prevalence of outcome in the exposed group / Prevalence of the outcome in the unexposed group

• The ratio of existing cases between those who are exposed and unexposed (used when frequency is prevalence)
• USE: Cross-sectional studies and population surveys

Question 3

What is ‘Risk Ratio’

Answer 3

Risk of outcome in exposed group / Risk of outcome in unexposed group

• Ratio that compares the risk of exposed and unexposed groups of getting an outcome.
• Same as prevalence as proportion but can only be applied to incident cases
• USE: Ecological or cohort studies

Question 4

What is ‘Odds Ratio of Exposure’?

Answer 4

Odds of exposure in those with the outcome / Odds of exposure in those without the outcome

• Ratio that compares the odds of exposure in those with and without the outcome
• USE: Case-control studies

Question 5

What is ‘Odds Ratio of Outcome’?

Answer 5

• Primarily used in logistic regression analysis - won’t need for exam

Odds of outcome in exposed groups / Odds of outcome in unexposed groups

Question 6

What is ‘Incidence Rate Ratio’?

Answer 6

Incidence rate of outcome in exposed group / Incidence rate of outcome in unexposed group

• Ratio that compares the incidence rate of an outcome in exposed and unexposed group
• USE: Ecological and cohort studies
• Need to know person time at risk