Table 2.

Criteria for validating a surrogate

Define patients, treatments, and clinical endpoints for which the potential surrogate applies. A strong statistical association between the surrogate and the clinical outcome of interest. Strong, consistent evidence of treatment differences in the surrogate for each trial. Treatment difference in clinical outcome within each trial is statistically explained by the surrogate. Across trials, magnitudes of treatment difference in the surrogate and in the clinical outcome are closely linked.