Although IRT has been recently used with some success in measuring alcohol dependence (e.g., Kahler et al., 2003; Krueger et al. 2004), such research is very preliminary. Research thus far has been limited in its theoretical linkage to a developmental course, with few tests of direct or moderating influences upon treatment outcome, and the impact of traitedness on severity assessment has not been tested. We used IRT to model an alcohol continuum and to compute both severity and traitedness coefficients for each participant in data from Project MATCH, an extensive alcohol-related dataset that includes treatment data from three interventions. We hypothesized that measuring both severity of alcoholism and traitedness of alcoholism using an IRT approach would enhance the measurement of alcohol severity and perhaps uncover treatment matching effects, both in Project MATCH and in subsequent investigations.
