What is a surrogate variable?

A surrogate variable is a type of measure that is used in clinical research to substitute for a direct measure of how a patient feels, functions, or survives. It often serves as an indirect indicator of clinical outcomes when direct measurements may be difficult to obtain or take a long time to assess. For example, in studies related to cardiovascular disease, blood pressure or cholesterol levels may be used as surrogate variables because they are easier to measure and can correlate with the actual health outcomes of interest, such as heart attacks or strokes.

Using surrogate variables can provide valuable insights in research settings, especially when evaluating the effectiveness of treatments during early stages or when assessing interventions that may take longer to manifest. Therefore, the correct choice highlights the role of surrogate variables as indicators of an indirect measurement of treatment effects.

In contrast, direct measures of clinical outcomes, continuous monitoring, and variables without practical applicability do not align with the defined concept of a surrogate variable, as they either focus on direct effects or failure to contribute meaningfully to research evidence.