proxy outcome, substitute outcome
Surrogate outcomes are proxy or substitute outcomes that are measured in a study because they are believed to reflect outcomes that are important.
They are often used because they are easier to measure than the important outcomes which they are believed to reflect.
To be relevant to patients, outcomes should measure treatment effects in terms that matter to patients, and not only in terms of indirect measures of importance.
There is often uncertainty about the extent to which an effect on a surrogate outcome reflects a corresponding effect on the important outcome.
For example, although blood pressure is not of direct relevance to patients, it is often used as an outcome in studies because it has been established that people with high blood pressure are more likely to have a stroke or heart attack than people with lower blood pressure. Surrogate outcomes are rarely as well established as blood pressure has been.
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