[Instrument for measuring psychological variables and adherence to treatment behavior in persons who are seropositive for HIV (VPAD-24)].

Objective: To test the psychometric properties of an instrument for measuring psychological variables and adherence to treatment behaviors in persons with HIV infection or AIDS.

Methods: A cross-sectional study was performed with 68 subjects who were seropositive for the human immunodeficiency virus (HIV) and who were being treated in a health facility in the city of Hermosillo (Sonora), Mexico, at the time the study was carried out. Five consecutive statistical testing procedures were applied for data analysis: the Student t test for comparison of means, for assessing the comprehensibility of the questions; an exploratory factorial analysis with varimax rotation for determining construct validity; Cronbach's alpha coefficient for determining reliability; Pearson's correlation coefficient (r) for assessing concurrent validity; and multiple linear regression for determining predictive value.

Results: In 25 out of a total of 30 questions, the Student t test for comparison of means gave statistical significance values of P < or = 0.05, P < or = 0.005, P < or = 0.01, and P < or = 0.001. A four-factor structure was found with the factorial analysis with varimax rotation: (1) current adherence behavior and treatment; (2) underlying reasons for adherence or lack of adherence; (3) psychological well-being and social competencies; (4) past adherence behavior with values above 1 that, taken as a whole, explain 65.50% of the variance. An overall alpha coefficient of 0.852 was obtained with the test for reliability. The test for concurrent validity showed correlations between factors 1 and 2 (r = 0.615; P < or = 0.01), between factor 2 and factors 3 and 4 (r = -0.178; P < 0.05 and r = 0.265; P < 0,05, respectively), and between factor 3 and duration of infection in months (r = 0.265; P < 0.05). Finally, multiple linear regression showed that psychological factors 2 and 4, which together explain 48.6% of the variance, predicted current adherence behavior (adjusted determination coefficient [R2] = 0.486).

Conclusion: According to the results obtained, the instrument has optimal reliability as well as construct validity, concurrent validity, and predictive validity.