To test the concurrent validity of alcohol trait severity, it was correlated with multiple measures used as matching variables in Project MATCH. Overall, the pattern of validity coefficients was very similar to that observed for other severity markers. In particular, alcohol trait severity as conceptualized using IRT did not generally appear to correlate more strongly than alcohol involvement. To test the incremental validity over the markers used in Project MATCH, partial correlations were computed between the alcohol trait severity score and concurrent variables after controlling for each of the severity markers used in Project MATCH (Table 3). Overall, these effects were limited; only 6 out of 51 (12%) incremental correlations were > .30, suggesting that the IRT-based score generally provides limited incremental information above and beyond additive scores derived from classical test theory methods for alcohol severity. To the extent that an IRT-based measure of alcohol severity did increment other measures, it did so with respect to AA involvement (average incremental r = .34), social functioning (−.27), and readiness for change (.34).
