An IRT-based measure of alcohol trait severity and the role of traitedness in trait validity: a reanalysis of Project MATCH data.

With the variability among alcohol users in mind, Project MATCH hypothesized several treatment matching relationships based on alcohol severity and alcohol dependence, but found limited effects. However, it is possible that the existing examinations of Project MATCH data did not fully characterize the nature of severity of alcohol dependence, as these analyses have examined dependence severity as an additive symptom count similar to the diagnostic strategy represented in the DSM-IV. We examined dependence severity as a latent trait hypothesized to have a characteristic developmental progression using Item Response Theory (IRT), and examined the implications of this approach to severity scaling in the Project MATCH data. The IRT-derived empirical continuum corresponded to an earlier theoretical model of the developmental course of alcoholism, demonstrated convergent and discriminant validity, and incremented other severity markers in predicting Alcoholics Anonymous involvement, social functioning, and readiness of change. However, it did not predict treatment outcomes or other validating variables more effectively than the measures used in the original design. Furthermore, an empirical index of person fit to this continuum did not moderate trait-validator relations including treatment outcome and treatment matching effects. Overall, findings did not support the incremental utility of a latent trait representation of alcohol severity.