OBJECTIVE: Motivational Interviewing (MI) can effectively stimulate motivation for health behavior change, but the active ingredients of MI are not well known. To help clinicians further stimulate motivation, they need to know the active ingredients of MI. A psychometrically sound instrument is required to identify those ingredients. The purpose of this study is to describe and evaluate the capability of existing instruments to reliably measure one or more potential active ingredients in the MI process between clients and MI-therapists.

METHODS: We systematically searched MedLine, Embase, Cinahl, PsycInfo, Cochrane Central, specialised websites and reference lists of selected articles.

RESULTS: We found 406 papers, 60 papers were retrieved for further evaluation, based on prespecified criteria. Seventeen instruments that were specifically designed to measure MI or aspects of MI were identified. Fifteen papers met all inclusion criteria, and reported on seven instruments that assess potential active ingredients of the interactive MI process. The capability of these instruments to measure potential active ingredients in detail and as a part of the interactive MI process varies considerably. Three of these instruments measure one or more potential active ingredients in a reliable and valid way.

CONCLUSION: To identify the potential active ingredients in the interactive MI process, a combination of the SCOPE (which measures potential technical active ingredients) and the GROMIT or the global ratings of the MISC2 (to measure potential relational ingredients) seems favourable.