Validation and Psychometric Properties of the Vietnamese Versions of the Test of Adherence to Inhalers (TAI) and Inhaler Medication Adherence Scale (IMAS) in Patients with Chronic Obstructive Pulmonary Disease

BACKGROUND: Reliable assessment of adherence to inhaled maintenance therapy is important in COPD management, yet no validated Vietnamese instruments have been available. This study translated and validated the Vietnamese versions of the Test of Adherence to Inhalers (TAI) and the Inhaler Medication Adherence Scale (IMAS). METHODS: A mixed-methods design was used. Phase 1 included forward-back translation, expert review, and cognitive testing to ensure semantic and cultural equivalence. Phase 2 was a cross-sectional survey of 210 clinically stable COPD patients at a tertiary outpatient clinic. Content validity, exploratory factor analysis (EFA), internal consistency, and four-week test-retest reliability were assessed. Content validity indexes were calculated from independent expert ratings using a four-point relevance scale. Associations with clinical indicators were examined using Spearman correlation. RESULTS: Content validity was high for both instruments (TAI S-CVI/Ave = 1.00; IMAS S-CVI/Ave = 0.96), and patient comprehension was excellent. EFA identified two components for the TAI, explaining 65.25% of variance, and four components for the IMAS, accounting for 74.27% of variance. Internal consistency was strong (TAI alpha = 0.87; IMAS alpha = 0.91), and reliability across age and symptom subgroups remained robust. Test-retest stability was high (ICC: TAI = 0.88; IMAS = 0.89). A moderate correlation between TAI and IMAS (rho = 0.43, p < 0.001) indicated that the two scales capture related but distinct behavioral and psychological aspects of adherence. CONCLUSION: The Vietnamese TAI and IMAS demonstrate good reliability, validity, and cultural suitability for assessing inhaler adherence in COPD. Their combined use may support routine evaluation, patient counseling, and adherence-focused research in Vietnam.