Validation study of the Brief Medication Adherence Scale (BMAS) in patients with schizophrenia and related disorders in Hong Kong

The purpose of this study was to develop and test an original self-rating instrument known as Brief Medication Adherence Scale (BMAS) to assess antipsychotic adherence level of Hong Kong Chinese patients with schizophrenia. On the interview day, BMAS and three other validated rating scales were given to local patients with schizophrenia and related disorders for completion. BMAS was required to fill in a second time after two weeks for the study of test-retest reliability. Results of BMAS were matched with those of other scales and blood level of prescribed mood stabilizers to test for construct validity. Data analysis was performed for 84 patients. Median BMAS scores recorded at both times were identical at 89/100, and a cutoff score of 70 was considered medication adherent with a sensitivity of 98.61% (CI 92.50%-99.96%). BMAS was positively and significantly correlated with the established Medication Adherence Rating Scale -Taiwanese (Spearman's ρ = 0.56, p < 0.05) and with variation in serum mood stabilizer level (Pearson's r = 0.55, p < 0.05). On the other hand, correlations with scales measuring mental condition and medication side effects were weak. Principal component analysis found two components (i.e. medication taking behaviors and attitudes) for the 10-question BMAS. Test-retest BMAS total scores were significantly correlated (intraclass correlation alpha = 0.87, p < 0.05), and Cronbach's alpha measuring internal consistency was 0.68. The current study confirms that BMAS is a valid and reliable scale that assesses medication adherence in patients with schizophrenia.