Abstract
Objective Are treatment effects on personality trait change ephemeral and attributable to change in clinical states? Data of an intervention study were used to examine if change in clinical states (e.g., stress or depression) accounts for change in personality traits and to test whether both changes in traits and clinical states were independently associated with substance use. Method Seventy-nine substance use patients (M-age = 25.3, SD = 2.7; 35% female) took part at a 4-week intervention and completed a total of 15 bi-monthly assessments across 28 weeks to measure change in traits and states during and after treatment. Results The results suggest that participants showed large trait and state changes over time, which happened rapidly with the majority occurring during the first four weeks. Trait and state changes were highly correlated, but not perfectly redundant. Significant variance in personality trait change remained after controlling for change in clinical states. Moreover, both trait and state change independently predicted substance use. Conclusion Personality trait change occurred relatively fast and was maintained until the last follow-up assessment six months after the end of the intervention. Also, the findings point to the notion that the conceptual distinction between traits and states may not be as important as originally thought.