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Table 2 Principal strata according to potential behavior in each source of noncompliance (alternative version of Table 1 )

From: Intermediate outcomes in randomized clinical trials: an introduction

Strata Behavior pattern in noncompliance sources 1, 2 and 3a Treatment assigned and received for subject R in corresponding stratum
Compliers Yes, no, no Ri(Ti) = Ti
  Yes, yes, no  
  Yes, yes, yes  
  Yes, no, yes  
Always takers No, yes, no Ri(Ti) = 1
  No, yes, yes  
  No, no, yes  
Never-takers No, no, no Ri(Ti) = 0
  1. *As the trial is blinded, there are no defiers, as subjects cannot systematically take the opposite treatment; **Ri = treatment received, Ti = treatment assigned (0 = placebo, 1 = calcium); 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.