Measuring drug dependence in police custody: An item response theory and differential item function analysis of UNCOPE in Australia

摘要

Abstract Introduction and Aims Although there has been significant investment in policies and programs aimed at preventing drug‐related crime, there has been comparatively little effort dedicated to the validation the relevant research and evidence gathering tools. In this study, we aim to confirm the internal consistency of UNCOPE, developed by Hoffmann and colleagues, in the Australian context, as well as explore whether time in custody and prior custodial experience results in differential item functioning. Design and Methods Data were derived from the Australian Institute of Criminology's Drug Use Monitoring in Australia Program in which the UNCOPE instrument had been administered with 15 454 detainees who reported illicit drug use in the past 12 months. Item response theory methods are used to explore the characteristics of all six items, while Multiple Indicators Multiple Causes and likelihood ratio differential item functioning test methods are used to explore differential item functioning. Results Strong support is indicated for the internal consistency of the UNCOPE instrument. Modest differential functioning is identified for only one item, indicating that prolonged periods of detention prior to interview may influence the probability of endorsement for items that require introspection and reflection on drug‐related neglect. These modest effects are unlikely to have any practical effect on the overall utility of UNCOPE. Discussion and Conclusions In these analyses, the item characteristics of UNCOPE appear consistent with results seen in the USA. Further, the modest differential item functioning identified for neglect (item N) has no practical impact on the overall functioning on UNCOPE. Criminal justice and drug policy researchers will be comforted by the absence of any substantial implementation or environmental bias.