What explains personality change intervention effects?

= 18-75), we implemented randomized online interventions of self-improvement or self-acceptance over a 3-month period, with another follow-up 6 months after baseline and a waitlist control group added in Study 2. Across Studies 1 and 2, participants in both intervention groups reduced discrepancies between current and ideal personality and increased in well-being. In both intervention groups, current personality increased, whereas ideal personality remained stable. Critically, however, control group participants changed similarly, with no significant differences in change compared to participants who received the interventions. Study 3 compared different control group specifications and highlighted that the intervention recruitment framing might have induced selection effects and expectancy and demand effects leading to positive changes in neuroticism, conscientiousness, and extraversion as well as life satisfaction and self-esteem. Thus, we demonstrate both shortcomings of previous intervention designs and imprecisions in theoretical frameworks of personality change mechanisms. We discuss future directions including multimethod studies, measurement advances, and microrandomization of intervention components. (PsycInfo Database Record (c) 2025 APA, all rights reserved).