Estimating Treatment Effects using Multiple Surrogates: The Role of the Surrogate Score and the Surrogate Index

Understand

Estimating the long-term effects of treatments is of interest in many fields.

• A common challenge in estimating such treatment effects is that long-term outcomes are unobserved in the time frame needed to make policy decisions.
• One approach to overcome this missing data problem is to analyze treatments effects on an intermediate outcome, often called a statistical surrogate, if it satisfies the condition that treatment and outcome are independent conditional on the statistical surrogate.
• The validity of the surrogacy condition is often controversial.