Module 4: Relative Risk & Odds Ratio

Relative Risk (cont'd)

Incidence of outcome with exposure RR = Incidence of outcome without exposure RR = 1 RR > 1 RR < 1

Odds ratio (OR)

a relative measure of effect, which allows the comparison of the intervention group of a study relative to the comparison or placebo group. Odds of exposure in those with disease OR = Odds of exposure in those without disease OR = 1 OR > 1 OR < 1

Relative Risk (RR)

is often used when the study involves comparing the likelihood, or chance, of an event occurring between two groups. Relative Risk utilizes the probability of an event occurring in one group compared to the probability of an event occurring in the other group.

Odds Ratio Example

• Case control study • Examined whether there were an increased odds of advanced maternal age among children with autism compared to children without autism. • OR = 1.38 for each 10-year increment in maternal age • OR = 1.38 for each 10-year increment in maternal age (1-1.38) x 100 = 0.38 x 100 = 38% Children with autism had a 38% increased odds of being born to a mother with advanced maternal age compared to children without autism

Relative Risk Example

• Prospective cohort study • Examined whether physical activity affects rates of death among women with breast cancer • RR = 0.80 Women who exercised 3 to 8.9 MET hours per week compared with women who engaged in less than 3 MET-hours per week (3 MET-hours is equal to walking at an average pace of 2 to 2.9 mph for 1 hour) • RR = 0.80 Women who exercised 3 to 8.9 MET-hours per week compared with women who engaged in less than 3 MET-hours per week (1-RR) x 100 = (1-0.8) x 100 = 0.2 x 100 = 20% Risk of death in women who exercised 3-8.9 MET hours per week was decreased by 20% relative to the women who exercised less than 3 MET-hours per week Prospective cohort study • Examined the risk of lung cancer death based on to smoking status • RR = 2.38 Men who were ex-smokers compared to never smokers • RR = 4.46 Men who were current smokers compared to never smokers RR = 2.38 Men who were ex-smokers compared to never smokers (1-RR) x 100 = (1-2.38) x 100 = 1.38 x 100 = 138% • Risk of lung cancer death among male ex-smokers is increased 138% compared to men who never smoked. • Lung cancer death is 2.38 times more likely to occur in male ex-smokers as compared to male never smokers