Surrogacy Case Study: Prostate Specific Antigen (PSA ... - Isped

Validation Criteria
R² trial =1: surrogate “perfect at the trial-level”
R² trial ≈1: surrogate “valid at the trial-level”
To be meaningful, a good surrogate must also
demonstrate high correlation at the individual
patient level (ie: be a strong prognostic factor)
Ref: Buyse et al, Biostatistics 2000;1:49.
• “how close” to 1 ?
• Computationally intensive
• Requires replicate trials of similar treatments