Keywords

Statistical dependence; therapists effects; intraclass correlation; power; psychotherapy research

Abstract

It is essential that outcome research permit clear conclusions to be drawn about the efficacy of interventions. The common practice of nesting therapists within conditions can pose important methodological challenges that affect interpretation, particularly if the study is not powered to account for the nested design. An obstacle to the optimal design of these studies is lack of data about the intraclass correlation coefficient (ICC), which measures the statistical dependencies introduced by nesting. To begin the development of a public database of ICC estimates, the authors report ICCs for a variety outcomes reported in 20 psychotherapy outcome studies. The magnitude of the N = 495 ICC estimates varied widely across measures and studies. The authors provide recommendations regarding how to select and aggregate ICC estimates for power calculations and show how researchers can use ICC estimates to choose the number of patients and therapists that will optimize power. Attention to these recommendations will strengthen the validity of inferences drawn from psychotherapy studies that nest therapists within conditions.

Document Type

Peer-Reviewed Article

Publication Date

2011

Language

English

College

Family, Home, and Social Sciences

Department

Psychology

Included in

Psychology Commons

Share

COinS