Baseline Addiction Severity Index (5th ed.; ASI-5) data of 2,142 substance abuse patients were analyzed with two nonparametric item response theory (NIRT) methods: Mokken scaling and conditional covariance techniques. Nine reliable and dimensionally homogeneous Recent Problem indexes emerged in the ASI-5's seven areas, including two each in the Employment/Support and Family/Social Relationships areas. Lifetime Problem indexes were derived for five of the areas--Medical, Drug, Alcohol, Legal, and Psychiatric--but not for the Employment/Support and Family/Social Relationships areas. Correlational analyses conducted on a subsample of 586 patients revealed the indexes for the seven areas to be largely independent. At least moderate correlations were obtained between the Recent and Lifetime indexes within each area where both existed. Concurrent validity analyses conducted on this same subsample found meaningful relationships, except for the Employment/Support area. NIRT-based methods were able to add to findings produced previously by classical psychometric methods and appear to offer promise for the psychometric analysis of complex, mixed-format instruments such as the ASI-5.
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