Using growth curves to determine the timing of booster sessions

Booster sessions are often recommended to reestablish or reinforce the cognitive messages or behavior changes due to therapeutic and behavioral interventions. To plan intervention-relevant booster sessions, researchers need to know the pattern(s) of individual change over time in outcome variables and for experimental groups. Growth curve analysis of repeated measures can estimate these patterns for different categories of intervention participants. This article demonstrates an application of this method using data from a recently completed multisite randomized experiment that compared 3 different counseling and testing methods for prevention of HIV infection and other sexually transmitted diseases, Project RESPECT. Reported self-efficacy for condom use with the main sexual partner is used as an illustrative example. For most experimental groups, self-efficacy for condom use declined for both female and male respondents soon after the intervention and booster sessions should have been instituted within 3 months after the intervention. The article closes with some recommendations for both prospective and retrospective use of growth curves to rationally plan the timing of booster sessions and to evaluate their effectiveness in preventing relapse.