In the proposed project, an IRT-derived Rasch model was used to scale items from several instruments (as discussed above) with respect to their ability to discriminate individuals at varying levels of alcoholic severity. These indicators were initially selected for their content: items from selected instruments that instantiated Jellinek’s 43 developmental markers of alcoholism represented the initial pool for consideration. This initial set of indicators was subsequently purified in an effort to construct a preliminary scale providing a unidimensional set of indicators. The papers by Kahler et al. (2002) and Krueger et al. (2004) provide useful illustrations of the application of similar procedures to alcohol data, although these authors did not have the opportunity to test their continua against an extensive set of external markers, including treatment outcome, which is afforded by the Project MATCH data.
