Measuring psychotherapist functioning with the Therapist Work Involvement Scales (TWIS): reliability, factor structure, and measurement invariance.

Objectives: The Therapist Work Involvement Scales (TWIS) is a self-report research instrument that enables a multilayered description of psychotherapists' experiences when treating clients. The TWIS was created in a comprehensive study of close to 5,000 psychotherapists, and has been used in multiple studies. The aim of the current paper is to clarify the organization and statistical characteristics of the TWIS, and to present an updated version for longitudinal and cross-sectional research.

Methods: Collection of a large sample of psychotherapy trainees made possible the use of confirmatory factor analysis (CFA) to evaluate the dimensions and structure of therapists' process experiences, assessing reliabilities, measurement invariance over gender, item statistics, and correlations with other measures to show concurrent and predictive validity.

Results: The CFAs largely confirmed the factor structure of four of the five facets, and of the global super-factors. The global factors of Healing Involvement and Stressful Involvement each showed substantial correlations with therapists' attachment style and professional growth, and were used to describe four practice patterns that typify the experiences of therapists.

Conclusion: The results have shown the TWIS to be a statistically sound, multidimensional research instrument enabling therapists to describe their experience in current therapeutic work.