Falling into nothingness: Modeling suicidal ideation as the person × situation interaction of personality functioning...

Suicidal ideation (SI) is understood to emerge usually from the interplay of stable vulnerabilities and fluctuating situational stressors. This study explicitly tested this notion by examining whether impairments in personality functioning moderate the relationship between momentary loneliness and SI in daily life. A total of 180 participants (N = 85 inpatients, N = 95 community members) completed a baseline assessment of personality functioning (Operationalized Psychodynamic Diagnosis Structure Questionnaire) and a signal-contingent 10-day ecological momentary assessment of loneliness and passive SI. Linear mixed-effects models disaggregated between- and within-person components of loneliness and examined both concurrent and lagged effects on SI, including interactions of within-person loneliness with personality functioning. There were 9,001 observations in total (M = 48.37, SD = 18.82, per participant). Impairments in personality functioning were associated with higher mean levels of loneliness and SI. At the same measurement point, within-person increases in loneliness were associated with heightened SI, particularly among individuals with more severe impairments in personality functioning. Prospective models failed to identify a significant lagged effect of loneliness or its interaction with personality functioning; only trait-level loneliness and the level of personality functioning remained predictive of subsequent SI. Findings support a Person × Situation interaction model of SI, indicating that experiences of loneliness are a particularly strong risk factor for SI for individuals with low levels of personality functioning. By integrating trait- and state-level perspectives on risk, ecological momentary assessment offers a promising tool for capturing dynamic processes and real-time, personalized intervention approaches. (PsycInfo Database Record (c) 2026 APA, all rights reserved).