Allegiance in psychotherapy outcome research: Separating association from bias.

Concern about the contamination of psychotherapy outcome studies by “allegiance bias”—distortion of findings because of investigators’ preferences—has led to the proposal that findings to date should not be used to make inferences about the relative efficacies of psychotherapies. It has also been proposed that results from all such studies should be adjusted to cancel the presumed distorting effects of allegiances. We argue that although much effort has been devoted towards establishing the existence of statistical associations between allegiances and outcomes, the causal implication—that investigators’ allegiances influence results—has gone virtually untested. We present a new vocabulary with the aim of sharpening the allegiance discourse, and we propose that research strategies markedly different from the ones used to date are needed to address some of the more serious limitations of allegiance bias research.