Surrogate endpoints in clinical trials

Surrogate endpoints are endpoints that are not directly related to the clinical outcome of interest but are used as a substitute for it. They are often used in clinical trials to assess the efficacy of a treatment when the actual clinical outcome may take a long time to observe or may be difficult to measure. For instance, in a trial for a new drug to treat high blood pressure, the surrogate endpoint may be the reduction in blood pressure rather than the actual clinical outcome of interest: reduction in the risk of heart attack, stroke, or death.

There are entire books written on surrogate endpoints, but the following are the main simplified points.