Intermediate outcomes in randomized clinical trials: an introduction

Table 1 Principal strata and sources of (non)compliance

	Experimental group (calcium)			Control group (placebo)
Source of (non) compliance^a	Taking >80% of tablets assigned	Physician indicated collateral treatment involving substantial calcium	Subject self-indication collateral treatment involving substantial calcium	Taking >80% of tablets assigned	Physician indicated collateral treatment involving substantial calcium	Subject self-indication collateral treatment involving substantial calcium
Strata
Compliers	Yes	No	No	Yes	No	No
	Yes	Yes	No	Yes	Yes	No
	Yes	Yes	Yes	Yes	Yes	Yes
Always- takers	Yes	No	Yes	Yes	No	Yes
	No	Yes	No	No	Yes	No
	No	Yes	Yes	No	Yes	Yes
	No	No	Yes	No	No	Yes
Never-takers	No	No	No	No	No	No
Defiers*

*As the trial is blinded, there are no defiers, as subjects cannot systematically take the opposite treatment. If a subject decides not to take the pills (treatment) assigned, she belongs to the never-takers stratum. Compliers are subjects who always take the treatment assigned.
^aSources of (non)compliance: 1, taking >80% of pills assigned; 2, collateral treatment involving substantial calcium indicated by physician; 3, self-indicated collateral treatment involving substantial calcium.

ISSN: 1745-6215