Psychometric Evaluation and Predictive Validity of an Adapted Adherence Self-Efficacy Scale for PrEP

Adherence to and sustainment of HIV pre-exposure prophylaxis (PrEP) are critical to its effectiveness. Adherence self-efficacy, i.e., confidence in one's ability to adhere to a particular medication, is a key psychological determinant of health behavior that strongly predicts HIV treatment adherence but has been understudied in PrEP research. This paper describes the psychometric evaluation and validation of the PrEP Adherence Self-Efficacy Scale (PrEP-ASES), adapted from the previously validated HIV Treatment Adherence Self-Efficacy Scale (HIV-ASES). Data are drawn from two studies conducted at a community health center, one focused on gay and bisexual cisgender men and the other on transgender women. Factor analyses support a one-factor score (eigenvalue = 6.78) that explained 75.3% of the variance, with good test-retest reliability (rs > 0.40). In both studies, higher PrEP-ASES scores were associated with PrEP uptake, adherence, and sustainment. Findings support the utility of the PrEP-ASES in research and suggest the importance of addressing self-efficacy in PrEP programs and services.