Symptoms as rapidly fluctuating over time: Revealing the close psychological interconnections among borderline personality disorder symptoms via within-person structures.

Despite the clinical emphasis on processes happening within individuals, investigations into the psychological, structural connections between mental health symptoms have almost exclusively analyzed differences between people. These investigations have revealed important findings; however, they do not reveal the close connections among symptoms in an individuals' psychology. This study thus examined the psychological connections between symptoms directly, using borderline personality disorder (BPD) symptoms as an example. Participants (252; 74 with BPD) reported their momentary BPD symptoms five times daily, and 165 did so again 18 months later. In support of personalized medicine (Wright & Woods, 2020), individuals' BPD symptom structures differed considerably from each other and from the between-person structure. A novel technique revealed that differences were greater than expected by chance. Within-person structures tended to exhibit more symptom granularity (more factors and lower variance explained) and differing symptom meanings (patterns of loadings). For example, some individuals exhibited close connections between relationship turmoil and identity uncertainty, whereas other individuals exhibited close connections between relationship turmoil and impulsivity. Thus, conceptions of any given person's psychopathological processes using between-person structural findings will most likely be inaccurate. (PsycInfo Database Record (c) 2021 APA, all rights reserved).