Therapists as fixed versus random effects-some statistical and conceptual issues: a comment on Siemer and Joormann (2003).
The authors disagree with M. Siemer and J. Joormann's assertion that therapist should be a fixed effect in psychotherapy treatment outcome studies. If treatment is properly standardized, therapist effects can be examined in preliminary tests and the therapist term deleted from analyses if such differences approach zero. If therapist effects are anticipated and either cannot be minimized through standardization or are specifically of interest because of the nature of the research question, the study has to be planned with adequate statistical power for including therapist as a random term. Simulation studies conducted by Siemer and Joormann confounded bias due to small sample size and inconsistent estimates.
Crits-Christoph
Paul
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Department of Psychiatry, University of Pennsylvania, Philadelphia, PA 19104, USA. crits@mail.med.upenn.edu
Tu
Xin
X
Gallop
Robert
R
D000704:Analysis of Variance; D015982:Bias; D006801:Humans; D016013:Likelihood Functions; D015233:Models, Statistical; D009010:Monte Carlo Method; D017063:Outcome Assessment, Health Care / Q000706:statistics & numerical data; D011594:Psychometrics / Q000706:statistics & numerical data*; D011613:Psychotherapy / Q000706:statistics & numerical data*; D016032:Randomized Controlled Trials as Topic / Q000523:psychology*; D015203:Reproducibility of Results