Psychometric Evaluation of the Reward Probability Index in Emerging Adult Drinkers

Objective: Diminished access to environmental rewards is an established risk factor for addiction and a focus of many effective treatment approaches. Nevertheless, there is inconsistency in measurement approaches and a need for a psychometrically sound measure. The Reward Probability Index (RPI; Carvalho, Behavior Therapy, 42, 2011, pp. 249-262) is a 20-item self-report rating scale that measures access to and ability to experience psychosocial reward. Method: The current studies sought to evaluate the psychometric properties of the RPI in 2 samples of emerging adult heavy drinkers. Results: In Study 1, exploratory factor analysis in a sample of 393 college student drinkers supported a 2-factor model of the RPI (Reward Probability and Environmental Suppressors) after removal of redundant items, and corresponding subscales demonstrated good internal consistency. In Study 2, confirmatory factor analysis with 602 emerging adult drinkers recruited from the community supported the 2-factor model as best fitting after removal of one poor indicator, although absolute fit was only adequate. This 2-factor model demonstrated configural, metric, and scalar invariance across non-college and college subgroups as well as Black and White subgroups. Study 2 also demonstrated that the revised RPI subscales showed significant associations with measures of substance-free activity participation and enjoyment, anhedonia, and depressive symptoms. Furthermore, the study revealed the RPI Environmental Suppressors subscale predicted alcohol-related problems (β = .25, p < .001) beyond demographic covariates, weekly drinking, and depressive symptoms. Conclusions: These studies provide evidence for the validity of the RPI as an efficient measure of access to reward among emerging adult heavy drinkers. Public Health Significance This study suggests that the Reward Probability Index may be useful for measuring emerging adults' access to and ability to experience reward and that more reward restricting experiences are associated with greater levels of alcohol problems.