These different conceptualizations of substance use disorders have implications for research and clinical practice. Where a dimensional model provides a better fit than a categorical model, it can provide richer information [33]. Within a unidimensional structure it is possible to apply item response theory analysis to distinguish which criteria perform best in terms of discriminating those who have the disorder versus those who don't, and whether the criteria represent all levels of the severity spectrum. Such analysis has yielded useful information about the performance of substance abuse and dependence criteria in the lead up to DSM-V, [17-21, 34, 35] leading to the likely exclusion of the legal criterion from substance use disorders in DSM-V. However the application of a dimensional model to the diagnosis will not provide valid information if it is not in fact a dimensional construct.
