Factor structure, internal reliability and construct validity of the Methadone Maintenance Treatment Stigma Mechanisms Scale (MMT-SMS)

Background and aim: Experience of stigma towards methadone maintenance treatment (MMT) may be a barrier to the use of this treatment by people with opioid use disorder. We evaluated the factor structure, internal reliability, construct and criterion validity of a theory-based stigma measure, the Methadone Maintenance Treatment Stigma Mechanisms Scale (MMT-SMS) and compared this with the Substance Use Stigma Mechanism Scale (SU-SMS). Design: Surveys at the beginning and end of a prospective study together with records of drug use and treatment attendance during that study. Setting: Community methadone clinic in the Northeastern USA. Participants: Ninety-three participants who were receiving MMT; the average daily methadone dose was 84.8 mg/day (standard deviation = 28.39 mg/day). Measurements: The MMT-SMS uses a self-report questionnaire to assess three dimensions reflecting experiences of anticipated (nine items), enacted (nine items) and internalized stigma (seven items) specifically related to receiving MMT. Anticipated and enacted scales include three stigma source subscales (family, employers, health care workers; three items each). Responses are recorded on a five-point Likert-type scale, then averaged to produce the MMT-SMS scale/subscale scores. The SU-SMS is a self-report questionnaire to assess experiences of anticipated, enacted and internalized stigma regarding substance use history. Both scales were administered at the final parent study visit. Other measures included were assessed in the parent study and used to assess life-time and recent MMT (e.g. current MMT dose) and drug use experiences (e.g. past 30-day heroin injection). Findings: The MMT-SMS demonstrated good internal reliability (α = 0.806–0.952 for components). Confirmatory factor analysis supported the seven-factor scale structure, distinguishing between experiences of anticipated, enacted and internalized stigma, and anticipated and enacted stigma source subscales (family, employers, health care workers) [root mean square error of approximation (RMSEA) = 0.076, 90% confidence interval (CI) = 0.061–0.090, P-close = 0.003; confirmatory fit index (CFI) = 0.974; Tucker–Lewis index (TLI) = 0.971]. Construct validity helped to distinguish the MMT-SMS from established substance use stigma constructs. Criterion validity observed associations with substance use experiences while on MMT, likely to predict future MMT success. Internalized MMT stigma was uniquely associated with daily MMT dose. Regarding criterion validity: anticipated MMT and enacted substance use stigma were associated with past 30-day heroin injection, MMT stigma uniquely associated with opioid use behaviors while receiving MMT, and substance use stigma broadly associated with injection-related behaviors. Conclusions: The Methadone Maintenance Treatment Stigma Mechanisms Scale appears to be a reliable measure of methadone maintenance treatment stigma with robust validity in a sample of people with opioid use disorders receiving methadone maintenance treatment.