The psychometric properties of the iowa personality disorder screen in methadone-maintained patients: an initial investigation.

The psychometric properties of the Iowa Personality Disorder Screen (IPDS) were examined in 150 methadone-maintained patients who completed measures of demographic, psychopathology, substance use, pain, and methadone maintenance treatment (MMT) characteristics. An exploratory factor analysis revealed a two-factor solution that explained 45% of the scale variance. The first factor captured internalizing tendencies, such as inhibition and hypersensitivity to others. The second factor comprised externalizing tendencies, such as impulsivity and insensitivity to others. The IPDS item subsets, derived factors, and the total score were significantly related to race/ethnicity but not sex. The effects of race/ethnicity were controlled statistically when the IPDS was compared to other measures of psychopathology, self-reported substance use, pain variables, and MMT characteristics. In general, the IPDS appears to be reliable and valid for use with methadone-maintained patients. The two-factor structure found in this study may have clinical utility and merits further investigation in other MMT samples.