When something happens after treatment starts

Patients die, cross over, have a device removed or take rescue medication. Each strategy for these events asks a different question of the same trial, and gives a different answer.

Further reading: ICH E9(R1) addendum on estimands and sensitivity analysis (2019); FDA adoption of E9(R1) as guidance; Kahan, Hindley, Edwards, Cro and Morris (2024), The estimands framework: a primer on the ICH E9(R1) addendum, BMJ 384:e076316. The trial, its patients and all rates are invented for teaching. Every true value is computed exactly from the teaching world's complete potential outcomes; the Kaplan-Meier curve is its large-sample limit, computed by numerical integration.