Psychometric performance of the perceived stigma of substance abuse scale (PSAS) among patients on methadone maintenance therapy in Vietnam.

BACKGROUND

People who inject drugs (PWID) and patients on methadone maintenance therapy (MMT) face severe stigma and discrimination. However, there are limited measures assessing stigma towards individuals with substance use disorders or MMT patients, particularly in Vietnam, and few studies have examined the psychometric properties of existing measures. This study aims to examine the performance of the eight-item Perceived Stigma of Substance Abuse Scale (PSAS), created in the United States, among a population of MMT patients in Vietnam.

METHODS

A cross-sectional survey was conducted among 400 adult patients enrolled in an urban MMT clinic. Substance use stigma was measured using the PSAS. We conducted confirmatory factor analysis (CFA) and assessed construct validity, reliability and known-group validity.

RESULTS

The original eight-item scale was unidimensional, but yielded mixed goodness-of-fit indicators. Ultimately, dropping two items and allowing the errors of the items related to childcare to correlate improved the goodness-of-fit indicators. (RMSEA = 0.025; CFI = 0.999; and SRMR = 0.018). The shortened scale demonstrated acceptable reliability (Cronbach's α = 0.766). The mean stigma scores were significantly higher among individuals not working, but did not significantly vary by length of time in MMT, marital status, education attainment, HIV status, depression, concurrent injection drug use or missed methadone dose.

CONCLUSIONS

The shortened six-item scale demonstrated good construct validity and acceptability reliability, but it did not demonstrate many a priori hypothesized known-group validity associations. Further research should consider a mixed-methods validation approach.