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.

[1]  D. A. Kenny,et al.  The effect of nonindependence on significance testing in dyadic research. , 1995 .

[2]  E. Frank,et al.  Generalized covariance‐adjusted canonical correlation analysis with application to psychiatry , 2003, Statistics in medicine.

[3]  Jim Mintz,et al.  Implications of therapist effects for the design and analysis of comparative studies of psychotherapies. , 1991 .

[4]  W. Miller,et al.  Therapist effects in three treatments for alcohol problems , 1998 .

[5]  G. Casella,et al.  Statistical Inference , 2003, Encyclopedia of Social Network Analysis and Mining.

[6]  L R Muenz,et al.  Psychosocial treatments for cocaine dependence: National Institute on Drug Abuse Collaborative Cocaine Treatment Study. , 1999, Archives of general psychiatry.

[7]  D. A. Kenny,et al.  Consequences of violating the independence assumption in analysis of variance. , 1986 .

[8]  S. R. Searle.  Linear Models , 1971 .

[9]  H. D. Patterson,et al.  Recovery of inter-block information when block sizes are unequal , 1971 .

[10]  B. Wampold,et al.  The consequence of ignoring a nested factor on measures of effect size in analysis of variance. , 2000, Psychological methods.

[11]  S. R. Searle.  Linear Models: Searle/Linear , 1997 .

[12]  A. Beck,et al.  Meta‐Analysis of Therapist Effects in Psychotherapy Outcome Studies , 1991 .

[13]  Jutta Joormann,et al.  Power and measures of effect size in analysis of variance with fixed versus random nested factors. , 2003, Psychological methods.

[14]  C. Martindale,et al.  The therapist-as-fixed-effect fallacy in psychotherapy research. , 1978, Journal of consulting and clinical psychology.