Measuring Patients' Acquisition of Therapy Skills in Psychotherapy for Depression: Assessing the CCTS-SR and the IPSS-SR

Objective: Valid and reliable instruments to measure therapy skills are necessary to investigate these skills as mechanisms of change in cognitive-behavioral therapy (CBT) and interpersonal psychotherapy (IPT) for depression. The authors tested two measures of the skills patients with depression acquire in CBT and IPT.
Methods: Using data from 202 Dutch patients with depression, the authors conducted a psychometric evaluation of the Dutch translation of the Competencies of Cognitive Therapy Scale–Self-Report (CCTS-SR) and an initial psychometric evaluation of the newly developed Interpersonal Psychotherapy Skills Scale–Self-Report (IPSS-SR).
Results: A confirmatory factor analysis (CFA) resulted in a fit outside the acceptable range for the one-factor model of the CCTS-SR. For the IPSS-SR, an exploratory factor analysis and a CFA led to a four-factor solution that provided the best fit compared with other models, although it remained outside the acceptable range. Both instruments showed excellent internal consistency. Correlations between the CCTS-SR and IPSS-SR were small to moderate. Fewer depressive symptoms and higher levels of behavioral activation were related to higher scores on the IPSS-SR and CCTS-SR, while higher levels of education and fewer dysfunctional thoughts were related to higher scores on the IPSS-SR.
Conclusions: Interpreting CBT and IPT skills as unidimensional concepts should be cautioned against until future studies have investigated the factor structure of the CCTS-SR and IPSS-SR across the course of CBT and IPT for depression. Further implications for psychometric research and future directions related to increasing knowledge about the role of therapy skills in psychotherapies for depression are discussed.