The Multitheoretical List of Therapeutic Interventions - 30 items (MULTI-30).

Objective: To develop a brief version of the Multitheoretical List of Therapeutic Interventions (MULTI-60) in order to decrease completion time burden by approximately half, while maintaining content coverage. Study 1 aimed to select 30 items. Study 2 aimed to examine the reliability and internal consistency of the MULTI-30. Study 3 aimed to validate the MULTI-30 and ensure content coverage. Method: In Study 1, the sample included 186 therapist and 255 patient MULTI ratings, and 164 ratings of sessions coded by trained observers. Internal consistency (Chronbach's alpha and McDonald's omega) was calculated and confirmatory factor analysis was conducted. Psychotherapy experts rated content relevance. Study 2 included a sample of 644 patient and 522 therapist ratings, and 793 codings of psychotherapy sessions. In Study 3, the sample included 33 codings of sessions. A series of regression analyses was conducted to examine replication of previously published findings using the MULTI-30. Results: The MULTI-30 was found valid, reliable, and internally consistent across 2564 ratings examined across the three studies presented. Conclusion: The MULTI-30 a brief and reliable process measure. Future studies are required for further validation. Clinical or methodological significance of this article: The MULTI-30, developed and validated in this study, is a valid, reliable, and cost-effective brief measure which could be used to assess patients, therapists, and observers' perceptions of use of interventions from eight major therapeutic approaches. The MULTI-30 could be used to examine the role of use of specific interventions on process and outcome of different treatment modalities. It could also be used as a clinical tool in teaching, training, and supervision.