The way I used to explain “as treated” vs “intent to treat”:
Under AT, you’re asking a question about biology: does this treatment make a difference when it’s applied rigorously to the tests and absolutely never to the controls?
Under ITT, you’re asking a question about the practice of medicine, under actual combat conditions: if we tell clinicians and patients to do something, and they follow instructions as imperfectly as ever, is this treatment still a good idea?
That is: ITT bakes in mistakes, noncompliance, weird patients, etc. on top of the basic scientific effect.
The way I used to explain “as treated” vs “intent to treat”:
Under AT, you’re asking a question about biology: does this treatment make a difference when it’s applied rigorously to the tests and absolutely never to the controls?
Under ITT, you’re asking a question about the practice of medicine, under actual combat conditions: if we tell clinicians and patients to do something, and they follow instructions as imperfectly as ever, is this treatment still a good idea?
That is: ITT bakes in mistakes, noncompliance, weird patients, etc. on top of the basic scientific effect.