Validation of the Medication Adherence Scale in Thais in Schizophrenic Patients

Abstract

Objective: To test the Medication Adherence Scale for Thais (MAST) in schizophrenic patients and to determine cut-off point for an adequate medication adherence (MA). Methods: Participants were 119 outpatients with schizophrenia in Suansaranrom Hospital with ≥ 6 months of antipsychotic treatment. Data were collected at Month 0 by interviewing the participants using the MAST, the MA scale for schizophrenic patients of Sathuporn Putkhao, the Schizophrenia Quality of Life Scale (SQLS), and the Brief Psychiatric Rating Scale (BPRS). The study also assessed MA at Month 0 by pill count. At the third month, the researchers assessed subjects using the BPRS, pill count, and the Marlowe-Crowne Social Desirability Scale (MCSDS) for measuring one’s tendency to conform others’ expectations. At the sixth month, researchers assessed the patients with the MAST, the BPRS, pill counts, and the SQLS. The ROC (receiver operator characteristics) curves was employed to assess measurement properties of the MAST. Results: Exploratory factor analysis of the MAST scores at Months 0 and 6 revealed the scale contained one dimension. Cronbach's Alphas of the MAST at Months 0 and 6 were 0.84 and 0.85, respectively. The correlation coefficient (r) of the MAST scores at Months 0 and 6 was 0.88 (P<0.001). The r between the MAST score at Month 0 and MA measured by pill count at Months 0, 3, and 6 were 0.75, 0.72, and 0.73, respectively (P<0.001). The r between the MAST score at Month 0 and MA score from Sathuporn Putkhao’s scale (measured at Month 0) was 0.64 (P<0.001). Construct validity was evident from r between the MAST score at Month 0 and the quality life as measured by the SQLS at months 0 and 6 (-0.27 to -0.43; high SQLS scores represented poor quality of life) (P<0.003). The r between MAST scores at Month 0 and the BPRS at Month 0 , 3 and 6 ranged from -0.19 to -0.45 (high BPRS scores reflects more psychiatric symptoms) (P<0.037). The MAST scores at Months 0 and 6 and MCSDS were correlated with r ​​of 0.28 and 0.30, respectively (P<0.002), indicating that patients with high social desirability reported a higher score on the MAST.  Using MA from the pill count at Months 0 and 6 as gold standard, area under the ROC curve was 0.85 and 0.88, respectively. Appropriate cut-off point was 36 (out of the full score of 40). The MAST scale had sensitivity and specificity at 73.91-80.00 and 72.92-77.88%, respectively. Ooverall predictive accuracy was 73-78%. Positive predictive value and the negative predictive value were 34.29-39.53%, and 92.11-96.43, respectively. Positive likelihood ratio and negative likelihood ratio were in the range of 2.73-3.62 and 0.26-0.36, respectively. Conclusion: In schizophrenic patients, the MAST scale shows good validity, reliability, sensitivity and specificity. Therefore, the measure could be used to assess MA in patients with this disease.