The HIV risk-taking behavior scale (HRBS) is an 11-item instrument designed to assess the risks of HIV infection due to self-reported injection-drug use and sexual behavior. A retrospective analysis was performed on HRBS data collected from approximately 1,000 participants pooled across seven clinical trials of pharmacotherapies for either the treatment of cocaine dependence or methamphetamine dependence. Analysis faced three important challenges. The sample contained a high proportion of missing assessments after randomization. Also, the HRBS scale consists of two distinct behavioral components which may or may not coincide in response patterns. In addition, distributions of responses on the subscales were highly concentrated at just a few values (e.g., 0, 6). To address these challenges, a single probit regression model was fit to three outcomes variables simultaneously – the two subscale totals plus an indicator variable for assessments not obtained (non-response). This joint-outcome regression model was able to identify that those who left assessment early had higher self-reported risk of injection-drug use and lower self-reported risky sexual behavior because the model was able to draw on information on associations among the three outcomes collectively. These findings were not identified in analyses performed on each outcome separately. No evidence for an effect of pharmacotherapies was observed, except to reduce missing assessments. Univariate-outcome modeling is not recommended for the HRBS.
Keywords: cocaine dependence, latent variables, methamphetamine dependence, missing assessment, multivariate outcome, probit regression
Citation: Holmes TH, Anderson AL, Li S-H and Elkashef AM (2011) Advantages of joint modeling of component HIV risk behaviors and non-response: application to randomized trials in cocaine-dependent and methamphetamine-dependent populations. Front. Psychiatry 2:41. doi: 10.3389/fpsyt.2011.00041
Received: 17 February 2011;
Paper pending published: 03 April 2011;
Accepted: 22 June 2011; Published online: 07 July 2011.
Edited by:Karl Goodkin, AIDS Healthcare Foundation, USA
Reviewed by:Mark Bradley, Columbia University, USA
Copyright: © 2011 Holmes, Anderson, Li and Elkashef. This is an open-access article subject to a non-exclusive license between the authors and Frontiers Media SA, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and other Frontiers conditions are complied with.
*Correspondence: Tyson H. Holmes, Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, 401 Quarry Road, MC 5718, Stanford, CA 94305-5718, USA. e-mail: email@example.com