The compliance score as a regressor in randomized trials

The compliance score in randomized trials is a measure of the effect of randomization on treatment received.It is in principle a group.level pretreatment variable and so can be used where individual.level measures of treatment received can produce misleading inferences.The interpretation of models with the compliance score as a regressor of interest depends on the link function.Using the identity link can lead to valid inference about the effects of treatment received even in the presence of nonrandom noncompliance; such inference is more problematic for nonlinear links.We illustrate these points with data from two randomized trials.