What is the investigator allegiance effect and what should we do about it?

The meta-analysis of Luborsky et al. (this issue) confirms the significance of an investigator allegiance effect in psychotherapy research and clarifi es the magnitude of this effect. In this commentary, I argue that the inves tigator allegiance is most likely a proxy measure of the expertise of the i nvestigator's team with the novel therapy and the disproportionately lower credibility and,integrity of the comparator condition. Hence, larger allegi ance effects are more likely early in the developmental history of research with newer therapies, that is, when pseudotherapies or nonspecific compara tors are commonly used. Studies that offer active comparators that are both credible and rigorously and professionally' administered are unlikely to s how an allegiance effect. Use of "blinded," independent evaluations of outc ome provides another safeguard. The investigator allegiance effect does not need to be an anathema to psychotherapy researchers.