Intervention-Induced Neuroticism Change Across Multiple Timescales

Neuroticism is one of the most consequential personality traits for individuals and society. Interventions that facilitate desired changes in this trait may thus have far-reaching benefits. Initial evidence supports that interventions can foster lasting neuroticism change, but the mechanisms, direction, and timing of these effects remain unclear. Although most personality theories posit that changes in broad, enduring personality traits are mediated via changes in momentary personality states and intermediary trait-relevant habits, there are few direct tests of this theorized bottom-up process. Using data from the Changing How I Live Life Study (N = 446), which examined a digital intervention to reduce neuroticism, we examined 1) the shape and magnitude of intervention-induced changes in neuroticism across three timescales, 2) the associations among these changes, and 3) whether these associations varied across intervention strategies targeting different levels of neuroticism. Changes in momentary neuroticism reliably predicted changes in daily and weekly measures of neuroticism and vice versa, and changes across all three timescales were correlated with changes in generalized trait neuroticism from pre- to post-intervention. Together, these results support the conceptual relevance and causal importance of both bottom-up (i.e., momentary, short-term → enduring, longer term) and top-down (i.e., enduring, long-term → momentary, short-term) processes of personality change. Overall, this study provided a key test of theoretical predictions about the process and directionality of intervention-induced personality change and, in doing so, helped elucidate the mechanisms of intentional personality change and generate insights about how to enhance intervention efficacy.