Measures of Association

Question 1

What is risk ratio?

Answer 1

Risk ratio = CI exposed / CI not exposed

Means how many times more likely.

Question 2

What is rate ratio?

Answer 2

Rate ratio = IR exposed / IR not exposed

Means how many times more likely.

Question 3

What is prevalence ratio?

Answer 3

Prevalence ratio = prevalence among exposed / prevalence among not exposed.
Means how many times more likely.

Question 4

What is odds ratio?

Answer 4

Odds ratio (case-control) = odds of having exposure among cases / odds of having exposure among controls

Odds ratio (cohort) = odds of having disease among exposed / odds of having disease among not exposed

Means how many times more likely the odds are.

Question 5

What is attributable risk? And whats population attributable risk?

Answer 5

Risk difference = (CI exposed - CI non exposed)

Rate difference = (IR exposed - IR non exposed)

Means how much extra. E.g. compared to those who never exposed, there is an extra X no of cases per X amount of people.

For population attributable risk, the equation is
Risk/rate difference = (CI/IR total - CI/IR non exposed)

Question 6

What is population attributable fraction?

Answer 6

PAF = (IR total - IR non exposed) / IR total * 100

PAF = Prevalence of exposed * (OR - 1) * 100

Means, X% of outcome in population can be attributed to exposure.