In a randomized clinical trial comparing surgical to medical management, the intention-to-treat principle would count any outcome experienced in the "surgery" arm against that treatment method, even if the outcome occurred in the interval between randomization and the actual surgical procedure. In effect, one of the risks of surgery is that attendant on waiting for an opening in the surgical schedule, or the possibility that an intervening medical event would require postponing the procedure. As a result, the ITT comparison can be viewed as assessing the difference in two policies of treatment, i.e., a glimpse at how well patients like the ones eligible for the trial would fare if surgical treatment (with all of its attendant delays and risks and chances for changing one's mind prior to going under the knife) were adopted as the general rule, compared to how they would fare if medical treatment (with its attendant risks of adverse experiences, drug interactions, poor compliance) were adopted. The ITT comparison gets at the potential effectiveness of a mode of treatment. It does not directly address the efficacy of the treatment, that is, how well the treatment--when it is actually applied as intended--affects the disease process. Of course, if there are only a few patients in the ITT population who are not also in the "as treated" population, then the ITT analysis addresses both effectiveness and efficacy.
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Original Message------
Consider a randomized clinical trial comparing surgery vs. medical therapy. Patients assigned to medical therapy start immediately. But, for the surgery patients, there may be a delay in scheduling and performing the surgery. Nevertheless, the primary outcome (e.g., relapse or death) may occur in the intervening period. Does ITT require us to count these events against surgery even though they occurred before it happened? Is there a literature supporting this view?
Thanks,
Jim R.
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James Rochon, PhD
Principal Statistical Scientist
Rho Federal Systems
6330 Quadrangle Dr.
Chapel Hill, NC 27517
(919) 595-6857