Abstract
Aim: The aim of this study was to evaluate the psychometric properties of a Swedish version of the Impaired Control Scale. Impaired control (IC) over alcohol consumption is a core symptom of alcohol use disorder and a predictor of treatment outcome, but measures of IC are not well utilised in clinical practice. Methods: The study comprised 250 individuals from a randomised controlled trial conducted at an adult outpatient addiction clinic in Sweden. The statistical analyses concern dimensionality, convergent and divergent validity, reliability, measurement invariance and sensitivity to change. Results: Regarding dimensionality, a principal component analysis of the standardised residuals from a Rasch model indicated some evidence of further dimensions underlying the responses in the Failed Control (FC) and Perceived Control (PC) parts. Two parallel items (12 and 22 respectively) seemed to drive potential multidimensionality. When these items were excluded, goodness of fit to one-dimensional models was improved. Tests of convergent and divergent validity showed that failed control had the strongest associations to impaired control and alcohol use disorder while the attempted control part was not associated with the construct of impaired control or alcohol use disorder. Conclusion: The present results show that the FC part is the most valid measure of the underlying construct of IC. In addition, FC had close to a large effect in regard to sensitivity to change. This suggests that the FC part has potential utility for use as an assessment and evaluation tool of treatment effect on impaired control of drinking.