TY - JOUR
T1 - Implications of Therapist Effects for the Design and Analysis of Comparative Studies of Psychotherapies
AU - Crits-Christoph, Paul
AU - Mintz, Jim
N1 - Copyright:
Copyright 2018 Elsevier B.V., All rights reserved.
PY - 1991/2
Y1 - 1991/2
N2 - Technical reasons are presented as to why therapist should be included as a random design factor in the nested analysis of (co)variance (AN[C]OVA) design commonly used in psychotherapy research. Incorrect specification of the ANOVA design can, under some circumstances, result in incorrect estimation of the error term, overly liberal F ratios, and an unacceptably high risk of Type I errors. Review of studies indicates that the great majority of investigators continue to ignore this issue. Computer simulation studies revealed that considerable bias can be introduced by not specifying therapist as a random term. Finally, a reanalysis is presented of data from 10 psychotherapy outcome studies that indicated that therapist effects vary considerably and at times can be large. More recent studies that implement better quality controls appear to demonstrate less variance due to therapist. The implications of these results for the design of future studies are discussed.
AB - Technical reasons are presented as to why therapist should be included as a random design factor in the nested analysis of (co)variance (AN[C]OVA) design commonly used in psychotherapy research. Incorrect specification of the ANOVA design can, under some circumstances, result in incorrect estimation of the error term, overly liberal F ratios, and an unacceptably high risk of Type I errors. Review of studies indicates that the great majority of investigators continue to ignore this issue. Computer simulation studies revealed that considerable bias can be introduced by not specifying therapist as a random term. Finally, a reanalysis is presented of data from 10 psychotherapy outcome studies that indicated that therapist effects vary considerably and at times can be large. More recent studies that implement better quality controls appear to demonstrate less variance due to therapist. The implications of these results for the design of future studies are discussed.
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U2 - 10.1037/0022-006X.59.1.20
DO - 10.1037/0022-006X.59.1.20
M3 - Article
C2 - 2002139
AN - SCOPUS:0026032314
VL - 59
SP - 20
EP - 26
JO - Journal of Consulting and Clinical Psychology
JF - Journal of Consulting and Clinical Psychology
SN - 0022-006X
IS - 1
ER -