Effects of a Theory-Based Smartphone Intervention to Decrease Neuroticism in the General Public

Many people wish to be less neurotic, and such decreases could have far-reaching benefits, but evidence on nonclinical interventions and change mechanisms is limited. Using a German-speaking, adult sample (N = 446), we conducted a 6-week, smartphone-based randomized controlled intervention to test effects of theory-based strategies targeting different neuroticism levels and aspects. Across groups, there were significant self-report effects (d_effect = -0.22 to -0.37) that persisted through a 2-month follow-up (d_effect = -0.16 to -0.33), and follow-up peer-report effects for one of two measures (d_effect = -0.18 to -0.30). Treatment-group comparisons indicated that state-level strategies fostered larger immediate (albeit shorter-lasting) effects, whereas habit-level strategies led to smaller initial declines that strengthened over time. Behavior-focused strategies, for states and especially habits, yielded particularly strong effects across assessment methods, both independently and incrementally. Our findings demonstrate that neuroticism can be changed within 6 weeks and provide insight into effective mechanisms of change.