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Keywords:

  • statistical methodology;
  • psychotherapy outcome;
  • randomized controlled trial

Background

The pairing of analysis of variance (ANOVA)-based analyses with designs lacking multiple measurement of client change may lead to conclusions that are inconsistent with theoretical expectations about how change will occur. Multilevel modeling (MLM), when used with multiple assessments of client outcomes, provides a flexible set of tools to analyze trajectories of client change.

Purpose

The authors present an overview of MLM and growth curve analysis as applied to psychotherapy outcome. Results from a simulated data set illustrate how MLM-specifically, growth curve analysis–can be used to test hypotheses from randomized clinical trials.

Results

Growth curve analyses were applied to simulated data from an experimental design (treatment versus control group) with multiple assessments of client distress and a client individual difference variable. Results of growth curve analyses confirmed what was found with a pretreatment/posttreatment repeated-measures ANOVA but provided additional information not available from the ANOVA framework.

Conclusions

Given its flexibility, MLM is the recommended method to assess patterns of change in studies of psychotherapy outcome.