Validation of the Full and Short-Form Self-Help Involvement Scale Against the Rasch Measurement Model.

BACKGROUND: Substance use disorders (SUDs) are one of the nation's most costly problems in terms of dollars, disability, and death. Self-help programs are among the varied recovery support options available to address SUD, and evaluation of these programs depends on good measurement. There exists an unmet need for a psychometrically sound, brief, efficient measure of self-help involvement for individuals with SUD that is valid across different substances and age-groups. METHODS: Using data from 2,101 persons presenting for SUD treatment, the full 21-item Global Appraisal of Individual Needs Self-Help Involvement Scale (SHIS) and a newly developed 11-item short-form version were validated against the Rasch measurement model and each other. Differential item functioning (DIF) was assessed by primary substance and age. RESULTS: Both versions met Rasch psychometric criteria. The full scale had minor misfit with no DIF for alcohol, marijuana, or opioids but a few instances of DIF for amphetamine and cocaine users as well as for age, in that youth tended to endorse several easier items more frequently than did adults. The 11-item short form had neither misfit nor DIF by substance and only minor DIF by age was highly correlated with the full version and was relatively more efficient. Criterion-related validity was supported for both. CONCLUSIONS: Both the long and short versions of SHIS are psychometrically sound measures of a more comprehensive conceptualization of self-help involvement for SUDs that can be used as part of an in-depth assessment or as a short measure that lessens respondent burden.