title: Is the allegiance effect an epiphenomenon of true efficacy differences between treatments? a meta-analysis.
abstract: Many meta-analyses of comparative outcome studies found a substantial association of researcher allegiance (RA) and relative treatment effects. Therefore, RA is regarded as a biasing factor in comparative outcome research (RA bias hypothesis). However, the RA bias hypothesis has been criticized as causality might be reversed. That is, RA might be a reflection of true efficacy differences between treatments (true efficacy hypothesis). Consequently, the RA-outcome association would not be indicative of bias but an epiphenomenon of true efficacy differences. This meta-analysis tested the validity of the true efficacy hypothesis. This was done by controlling the RA-outcome association for true efficacy differences by restricting analysis to direct comparisons of treatments with equivalent efficacy. We included direct comparisons of different versions of trauma-focused therapy (TFT) in the treatment of posttraumatic stress disorder (PTSD). RA was measured from the research reports. Relative effect sizes for symptoms of PTSD were calculated. Random effects meta-regression was conducted. Twenty-nine comparisons of TFTs from 20 studies were identified. Initial heterogeneity among relative effect sizes was low. RA was a significant predictor of outcome and explained 12% of the variance in outcomes. The true efficacy hypothesis predicted the RA-outcome association to be zero; however, a substantial association was found. Thus, this study does not support the true efficacy hypothesis. Given findings from psychotherapy research and other fields that support a biasing influence of researcher preferences, RA should be regarded as a causal factor and conceptualized as a threat to the validity of conclusions from comparative outcome studies.
authors.affiliation: Institute of Social and Preventive Medicine, University of Bern, Switzerland. tmunder@ispm.unibe.ch
authors.forename: Thomas
authors.initials: T
authors.lastname: Munder
authors.forename: Christoph
authors.initials: C
authors.lastname: Flückiger
authors.forename: Heike
authors.initials: H
authors.lastname: Gerger
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Wampold
authors.forename: Jürgen
authors.initials: J
authors.lastname: Barth
mesh_terms: D015982:Bias; D015984:Causality; D057186:Comparative Effectiveness Research / Q000706:statistics & numerical data*; D006801:Humans; D007400:Interprofessional Relations; D011613:Psychotherapy; D016032:Randomized Controlled Trials as Topic; D012044:Regression Analysis; D012108:Research Personnel; D013313:Stress Disorders, Post-Traumatic / Q000534:rehabilitation*