Assessment of motivational interviewing: Psychometric characteristics of the MITS 2.1 in general practice

•This study added positive validity evidence to the adjusted MITS 2.1.•For high stakes assessment two coders and seven consultations suffice.•The MITS can be used to assess MI when consultations are relatively short.•The MITS can be used when consultations are partly dedicated to behaviour change.•Experienced coders are needed. Motivational Interviewing (MI) is increasingly used in healthcare. The Motivational Interviewing Target Scheme 2.1 (MITS) can be used to assess MI in short consultations. This quantitative validation study is a sequel to a qualitative study, which showed that the MITS is suitable for low-stakes assessment. We collected validity evidence to determine whether its suitability for high-stakes assessment in the GP-setting. Consultations of GPs and GP-trainees were assessed using the MITS. The internal structure was studied using generalizability theory; intra class correlation (ICC), convergent and divergent validity was determined. Two coders and seven consultations were found to be necessary for high stakes assessment. We found higher ICCs as coders were more experienced. Convergent validity was found; results for divergent validity were mixed. The MITS is a suitable instrument for high-stakes MI assessments in GP-setting. The number of consultations and coders that are needed for assessment are comparable to other instruments for assessing communication skills. The MITS can be used to assess conversations for their MI consistency in GP-setting where most consultations are relatively short and are only partially dedicated to behaviour change. As the MITS assesses complex communication skills, experienced coders are needed.