Effects of intervention attrition and research attrition on the evaluation of an HIV prevention program

Attrition impacts the effectiveness of preventive interventions as well as the external validity of efficacy analyses, This paper examines attrition from the intervention and from the research data collection in an HIV prevention program for out-of-treatment drug users. Of the 1,115 respondents, 87% completed the two-session HIV prevention intervention and of these 69% completed the 6-month data collection, Factors related to completing the intervention were different from those related to completing the 6-month interview, Completing the intervention was associated with HIV risk behaviors and with having a negative result on the project's HIV test, whereas research completion was related to indicators of a stable lifestyle, individuals at highest risk were less likely to complete the data collection and so were under-represented in the assessment of intervention efficacy. These results have implications for program planners and evaluators.