Longitudinal Changes in Maladaptive Personality Domains and Clinical Outcomes: A Study Protocol

Background : Maladaptive personality traits are transdiagnostic risk factors associated with functional impairment, lower treatment efficacy, and poor mental health outcomes. These traits, encompassing domains such as Negative Affectivity, Detachment, Antagonism, Disinhibition, Psychoticism, and Anankastia, contribute to difficulties in emotional regulation, interpersonal relationships, and occupational functioning. Despite growing evidence that personality traits can change over time, longitudinal research examining within-person fluctuations in maladaptive traits during psychotherapy remains scarce. This study protocol outlines a longitudinal research project aimed at investigating the dynamic interplay between maladaptive personality domains and treatment outcomes in a clinical sample undergoing Cognitive Behavioral Therapy. By examining both within-person fluctuations and between-person differences over multiple time points, this study seeks to clarify how personality change relates to symptom improvement and psychosocial functioning, addressing a critical gap in the literature. Methods : This preregistered longitudinal study will recruit patients from inTHERAPY, an Italian psychotherapy service specializing in Cognitive Behavioral Therapy. A total of 200 participants will be assessed across five time points (baseline, 3, 6, 9, and 12 months). Personality domains and clinical symptoms will be systematically evaluated throughout treatment to track individual trajectories of change. Data will be analyzed using Random Intercept Cross-Lagged Panel Models to investigate reciprocal relationships between personality domains and clinical outcomes, distinguishing between between-person differences and within-person fluctuations and Linear Growth Curve Models to examine mean-level change in maladaptive personality domains over time. An exploratory analysis will also be conducted to assess whether patients tend to show the greatest change in the personality domains most elevated at baseline. Discussion: Understanding the temporal interplay between maladaptive personality domains and clinical outcomes could provide valuable insights for personalized psychotherapy. Identifying which personality domains change most significantly during Cognitive Behavioral Therapy - and whether such changes predict symptom improvement - may inform the development of more targeted interventions. Furthermore, this study’s findings could enhance clinical decision-making by identifying key personality factors influencing therapy trajectories, ultimately improving treatment planning for individuals with impaired maladaptive personality domains.