Statistical Notes for Clinical Researchers: Definition and Comparison of Risk and Odds

One of the most frequently used outcomes in health studies is the status of disease, such as having disease or not having disease. A probability of having a disease is referred as a risk of a disease, as a basic term used in description of such a binary disease state. Also risk difference or risk ratio is used in comparison of risks among two or more groups. Different from risk, an odds by itself is not as frequently mentioned as risk. However odds ratio meaning ratio of two odds is very popular because it is the same value with an exponentiated regression coefficient from a logistic regression, i.e., exp(beta). To understand concept and usage of risk- and odds-related terms better, we will first talk about risk and odds briefly in this section.