Investigator allegiance and the evaluation of psychotherapy outcome research

Jeffrey S. Berman, Catherine M. Reich

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


Considerable evidence has demonstrated that the beliefs of researchers can inadvertently influence research findings. The possibility of this type of bias is of special concern in studies evaluating the outcome of psychotherapy, where investigators frequently have marked allegiances to particular therapies and these allegiances have been found to correlate substantially with the pattern of results. In this article we discuss the evidence concerning investigator allegiance in psychotherapy research, emphasize the need to distinguish between this factor as a potential confound and a proved causal effect, and outline strategies that have been suggested for researchers to minimize the potential for bias both when designing future research and drawing conclusions from existing evidence.

Original languageEnglish (US)
Pages (from-to)11-21
Number of pages11
JournalEuropean Journal of Psychotherapy and Counselling
Issue number1
StatePublished - Mar 2010

Bibliographical note

Funding Information:
This research was supported by a Centers of Excellence grant awarded to the Department of Psychology at the University of Memphis by the state of Tennessee.


  • Clinical trials
  • Experimenter bias
  • Investigator allegiance
  • Psychotherapeutic outcomes
  • Treatment effectiveness evaluation


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