Baseline and Daily Predictors of Negative Affect Dynamics in Patients Diagnosed with Borderline Personality Disorder: Specific Effects on Daily Means, Instability, and Inertia

Background Negative affect is a core clinical feature of Borderline Personality Disorder (BPD). Identifying baseline characteristics and day-to-day processes that predict negative affect dynamics is key for improving treatment strategies and refining the conceptualization of the disorder. Objective This study examined how baseline characteristics (psychiatric history, depressive symptoms, BPD severity, personality functioning) and daily processes (interpersonal hypersensitivity, self-criticism, self-concept stability) relate to daily negative affect levels, instability, and inertia in 45 individuals with BPD, assessed via Ecological Momentary Assessment (EMA) Method Participants (n = 45) recruited from clinical services in Santiago, Chile completed baseline self-report measures (PHQ-9, ZAN-BPD, LPFS-BF), and demographics including age of onset and basic psychiatric history. Over 11 days, EMA prompts were delivered at varying intervals under three randomized schedules (25/day every 30 min, 13/day every hour, 5/day every three hours), assessing negative affect, interpersonal problems, self-concept stability, and self-criticism. Multilevel linear mixed models examined predictors of mean daily negative affect. Two additional mixed-effects models explored daily dynamics: an inertia model (predicting negative affect at one moment from the previous moment) and an instability model (mean squared successive difference, MSSD). Results Baseline trait-like variables did not predict mean daily negative affect. Daily averages of interpersonal hypersensitivity and self-criticism predicted daily negative affect at both within- and between-subject levels. Inertia analyses indicated that persistence of negative affect was predicted by self-criticism but not by interpersonal hypersensitivity. Conversely, instability of negative affect was predicted by interpersonal hypersensitivity but not by self-criticism. Conclusions Daily fluctuations in negative affect in BPD appear more strongly tied to situational stressors than to stable traits, highlighting the importance of context-sensitive assessment and intervention. Self-criticism is linked to persistence of negative affect, whereas interpersonal hypersensitivity is associated with its instability.