Interpreting Odds and Risk and Understanding the Difference: Evidence in Practice

Categorical outcomes are most often reported in terms of relative risk or odds ratios. Interpreting what these metrics mean can be difficult for clinicians, and researchers often make mistakes in published papers. Key points to understand include: odds ratios cannot be interpreted in terms of likelihood of an outcome, in fact they have no intuitive meaning for a patient, relative risks and odds ratios are heavily influenced by how common or rare the outcome is, and an odds ratio will always be larger than a risk ratio from the same data.

Odds ratios and risk ratios are common summary statistics used to quantify between group differences or associations for categorical outcomes. These metrics are frequently misinterpreted by readers and researchers. This article will explain how the metrics are calculated and provide tips for interpreting and using them in the clinic.