Application of the Transtheoretical Model of change: psychometric properties of leading measures in patients with co-occurring drug abuse and severe mental illness.

People with severe mental illness (SMI) have high rates of substance use disorders. The Transtheoretical Model (TTM) is a framework for understanding behavior change. There are five leading measures associated with the TTM - University of Rhode Island Change Assessment, Processes of Change Scale, Decisional Balance Scale, Abstinence Self-Efficacy Scale, and Temptation to Use Drugs Scale. While these measures have been found to be reliable and valid in primary substance abusers, it is unknown if these measures are relevant in people with co-occurring SMI and substance use disorders (SUD). We evaluated the psychometric properties of these measures in a sample (n=240) of people with co-occurring disorders. Participants met DSM-IV criteria for schizophrenia/schizoaffective disorder or non-psychotic affective disorder, and current cocaine dependence or cocaine dependence in remission. All subscales showed good reliability and validity in the total sample. Analyses within diagnostic groups showed good reliability and validity in most groups, with some falling off in the affective disorders and remitted cocaine dependence groups. Overall, findings support the use of these measures in people with co-occurring disorders.