Psychometric re-evaluation of the immunosuppressant therapy adherence scale among solid-organ transplant recipients

Rationale The objective of this study was to conduct a psychometric re-evaluation of the immunosuppressant therapy adherence scale (ITAS), a self-report measure of immunosuppressant therapy (IST) adherence targeted to solid-organ transplant recipients. Methods Mailed questionnaires were used to collect data from 141 transplant recipients. A factor analysis of the ITAS was conducted. Validity was examined via Pearson's product-moment correlations (r) to theoretically tied measures of social support and resilience. Cronbach's and split-half alpha coefficients determined internal consistency. Results The response rate was 72.3%. The aggregate mean on ITAS' summed scores was 11.0 (standard deviation = 1.7). The single IST adherence factor had an eigenvalue of 2.92 and accounted for 73% of the scale items' variance. Component loadings for ITAS items were high (>= 0.80). Zero-order correlations among scale items were moderately strong (>= 0.57) and significant (P < 0.01). ITAS summed scores were significantly associated with measures of social support and resilience (r >= 0.20, P < 0.05). Cronbach's alpha was 0.87. The Guttman split-half coefficient was 0.90. Conclusions This re-evaluation provides needed confirmation that the ITAS is a valid and reliable measure of IST adherence. The ITAS may be useful as an IST adherence measure in the outpatient transplant clinic setting as it is easy to administer, brief and less expensive than many other adherence measures.