process to determine whether the effect on the surrogate predicts the effect on the intended final outcome. A validated surrogate endpoint is supported by a biological plausibility rationale and/or statistical confirmation of a strong association between trial treatment effect on the surrogate outcome and treatment effect on patient/participant relevant final outcome.
For example, blood pressure reduction is a validated surrogate endpoint for reduction of stroke and heart attacks; blood sugar reduction (HbA1c) is a validated surrogate for certain diabetes related complications; uric acid reduction is a validated surrogate endpoint for improvement of gout symptoms (http://www.ncbi.nlm.nih.gov/books/NBK326791/)