Adolescence is characterized by heightened sensitivity to social belonging, making loneliness prevalent and consequential for youth. Maladaptive personality traits may further exacerbate loneliness. In this preregistered 14-day Ecological Momentary Assessment study, we examined loneliness across social contexts and timescales in relation to maladaptive personality traits among N = 294 adolescents aged 12–21 years (Mage = 17.5, SD = 2.64; 58.5% female; 86.73% born in Germany). Participants answered 27,503 of 32,340 momentary prompts, indicating high compliance (85.1%). Loneliness (βmomentary = 0.51; βdaily = 0.67) was higher when participants were alone, yet only the presence of close others (e.g., friends) – not weaker ties (e.g., classmates) – reduced loneliness (β = –0.39 to –0.62). Youth who were alone more frequently did not report higher overall loneliness. Maladaptive personality traits were associated with higher (βmomentary = 0.32; βend-of-day = 0.40) and more variable (βmomentary = 0.31; βend-of-day = 0.34) loneliness but amplified the effect of being alone on loneliness only on the between-person level (β = –1.13). Exploratory analyses indicated that social satisfaction partially mediated the association (β = 0.50). These findings underscore the importance of both structural and qualitative aspects of social environments, as well as personality-related vulnerabilities, to better understand loneliness dynamics in youth.

A new multiple indicator multilevel latent state-trait (LST) model for the analysis of multitrait–multimethod–multioccasion (MTMM-MO) data is proposed. The LST-COM model combines current CFA-MTMM modeling approaches of interchangeable and structurally different methods and LST modeling approaches. The model enables researchers to specify construct and method factors on the level of time-stable (trait) as well as time-variable (occasion-specific) latent variables and analyze the convergent and discriminant validity among different rater groups across time. The statistical performance of the model is scrutinized by a simulation study and guidelines for empirical applications are provided.

Longitudinal studies exploring the role of early personality vulnerabilities as risk factors for later NSSI dynamics are scarce. In this study, we assess how pre-adolescent borderline personality pathology (BPP) traits (assessed at mean age 12.78; SDage = 1.38, age range = 7.17–14.78) shape dynamic links between daily socio-emotional dysregulation and NSSI thoughts during emerging adulthood (Mage = 20.96, SDage = 1.63). Mothers of 131 children completed questionnaires about their child’s BPP traits in pre-adolescence. These children were re-assessed eight years later and were asked to complete a daily diary for 14 consecutive days. During these 14 days, behavioral and emotional dysregulation as well as NSSI thoughts were self-reported. Multilevel structural equation modeling was used (1) to examine dynamic links between socio-emotional dysregulation manifestations and NSSI thoughts in early adulthood, and (2) to explore the role of pre-adolescent BPP traits in moderating these early-adult dynamic associations. Our findings suggest that young adults who were described by their mothers as high on BPP traits (especially anxious and paranoid traits) during pre-adolescence, tended to respond more with NSSI thoughts when experiencing dysregulation or when perceiving others as rejecting in young adulthood. Results are discussed in terms of potential targets for indicated prevention of NSSI development.