Measuring readiness-to-change substance misuse among psychiatric outpatients: I. Reliability and validity of self-report measures

Objective: The high rates of comorbid substance use disorders among persons living with severe and persistent mental illness (SPMI) have increased interest in assessing and enhancing motivation to change substance misuse in this population. This study provides evidence for the psychometric adequacy of three self-report measures of readiness-to-change. Method: The sample consisted of 84 persons (65% men) with co-occurring substance abuse or dependence and an SPMI. After a psychiatric assessment, participants completed three measures of readiness-to-change, which yielded seven subscales: (1) the Stages of Change Readiness and Treatment Eagerness Scale (ambivalence about change, recognition of substance-related problems, taking steps), (2) Decisional Balance Scale (pros of using, cons of using) and (3) the Alcohol and Drug Consequences Questionnaire (costs of quitting, benefits of quitting). Results: All of the subscales were stable over time, and 6 of the 7 subscales demonstrated excellent internal consistency. Reliability indices were comparable when analyses were repeated on subsets of participants defined by diagnosis, cognitive function, positive symptoms and negative symptoms. A pattern of theoretically meaningful intercorrelations provided convergent evidence of validity, and a general lack of relationships with demographic variables and indices of psychiatric status provided discriminant evidence of validity. Conclusions: These findings support efforts to quantify readiness-to-change substance misuse among persons with an SPMI.