Exploring individual differences in volitional personality state and trait change: The role of motivation and engagement during a 12-week intervention

Recent studies suggest that personality traits can change through interventions, but little is known about what drives individual differences in intervention gains. Based on personality development and intervention frameworks, we examined whether achieved personality state changes explain differences in trait change and whether these could be explained by participants’ motivation and intervention engagement. The study was based on a 12-week personality intervention with a total of 956 participants, daily and weekly state measures, and trait self- and observer-reports. Participants who showed stronger state deviations from the initial trait level changed more in their traits in the corresponding direction. Both state and trait changes were stronger if participants were more committed to their change goal, completed more implementation intentions, and enjoyed their implementations more (i.e., reinforcement). In contrast, the strength of the desire to change, expected attainability, and beliefs in the changeability of personality had no consistent effects—but individual differences were limited as most participants scored highly on these motivational aspects. The control group exhibited no mean-level changes or effects of any of these covariates. Taken together, these findings support key components of volitional change theories and can help guide future personalized intervention efforts.