Glossary
Surrogate endpoint.
Direct answer
A surrogate endpoint is an easily measured quantity recorded in place of the outcome genuinely sought, such as a laboratory value instead of lifespan or working capacity. This shortcut saves time and money, but it is worth no more than the demonstrated link between the stand-in and the real target.
The classic error is to assume that improving the stand-in improves the real state. That does not always hold, because a measure acts through several pathways that may cancel each other out. A surrogate is acceptable only once studies have shown that changes in it predict the outcome that actually counts.
In horses, radiographic findings, inflammatory markers and gait analysis often stand in for what owners care about: pain-free use and a long career. Radiographic appearance and clinical picture are well known not to agree in every case. In human medicine, blood pressure and laboratory values play the same double-edged role.
The evidence letter
Once a month: new syntheses, checked studies, and what has changed in the state of the evidence.