Definition The Odds Ratio is a measure of association which compares the odds of disease of those exposed to the odds of disease those unexposed Formulae OR = (odds of disease in exposed) / (odds of disease in the nonexposed) Example I often think food poisoning is a good scenario to consider when interpretting ORs Imagine a group of friends went out toOdds is the number having the outcome divided by the number not having the outcome The risk or odds ratio is the risk or odds in the exposed group divided by the risk or odds in the control group A risk or odds ratio = 1 indicates no difference between the groupsOdds ratios (OR) are commonly reported in the medical literature as the measure of association between exposure and outcome However, it is relative risk that people more intuitively understand as a measure of association Relative risk can be directly determined in a cohort study by calculating a risk ratio (RR)
3 5 Bias Confounding And Effect Modification Stat 507
