Assessing intervention efficacy: An example based on change profiles of unprotected sex among drug users

Over 700 active drug users recruited in East Harlem, New York City, to participate in an AIDS prevention project were interviewed on two occasions, 6 months apart, to assess changes in HIV-related risk behaviors. This paper presents an example of a method for analyzing patterns of risk behavior change over time as a means of comparing the effectiveness of two interventions. Results described in this paper focus on the number of unprotected sex acts reported in the 30 days prior to each interview and reflect five distinct patterns of risk level over time (i.e., a decrease, an increase, remaining at low risk, remaining at high risk, or no sexual activity at either time). Bivariate and multivariate analyses indicated that (1) compared to persons at high levels of unprotected sex at follow-up (time 2), those who remained at a low level or decreased were more likely to be HIV positive; and (2) age, living alone, and having a stable source of income were also significant predictors of risk pattern. Risk pattern was not associated with type of risk reduction intervention (standard or enhanced) or with drug treatment (yes or no) between baseline and follow-up. Implications of the findings were discussed with respect to (a) the assessment of efficacy of AIDS prevention interventions and (b) the analysis of risk behavior changes over time.