August 9, 2012
The Reducing Risky Relationships HIV (RRR-HIV) intervention was designed to decrease incorrect and dangerous thoughts about relationships in order to reduce risky sexual behavior among women being released from prison. Results showed that women who participated in the program engaged in less unprotected sex.
For future interventions, it is important to determine why this happened. Was it because, as hypothesized, the intervention changed their beliefs about relationships? Was it because the intervention reduced their substance use? Or were other factors at work? In a recent paper in the journal Nursing Research, Methodology Center Investigators Donna Coffman and Kari Kugler used propensity score methods to estimate the causal effect of the RRR-HIV intervention on unprotected sex. These methods are broadly applicable to measuring the impact of interventions that target a mediator in order to achieve a healthy outcome.
In this study, treatment is the RRR-HIV intervention, a randomized intervention designed to reduce risky relationship thoughts. The researchers measured risky relationship thoughts, substance use, risky sexual behavior, and unprotected sex 30 days after the intervention; they measured unprotected sex 90 days after the intervention. Risky relationship thoughts were the mediator and unprotected sex was the outcome.
The authors found the intervention resulted in a significant decrease in risky relationship thoughts and that risky relationship thoughts resulted in an increase in unprotected sex. By reducing bias, propensity score models improve the accuracy of statistical analysis of interventions with mediators and allow researchers to determine not only whether their intervention works but also how it works.
This article is the basis of the causal mediation example page on our website. Visit that page for more non-technical details.
Coffman, D. L., & Kugler, K. C. (2012). Causal mediation of a human immunodeficiency virus preventive intervention. Nursing Research, 61(3) 224-230. PMCID: PMC3377683
View full-text article at Nursing Research.