In the current study, the investigators want to give the ageing context the attention it deserves by examining whether the AMPD and ICD-11 approach is appropriate for use in older adults. This will happen by means of two central objectives, each divided in different research questions.

1. The first central objective is the validation of the AMPD and ICD-11 conceptualization of PDs and its corresponding instruments, in older adults. Even though early research shows promising results for the use of dimensional classification in older adults, both of the questionnaires were originally developed and validated in younger adult samples. Therefore, this research is interested in the examination of the model and its corresponding instruments in older adults. The two instruments that will be used in the study are the Level of Personality Functioning Scale - Brief Version 2.0 (LPFS-BF 2.0) (Weekers et al., 2018) and the Personality Inventory for DSM-5 - Brief Version Modified (PID-5-BF+M) (Bach et al., 2020), which measure criterion A and criterion B, respectively. In this study, the abbreviated version of both questionnaires were chosen, in order not to unnecessarily burden the older participants.

   Firstly, the construct validity of the questionnaires in the general population will be examined. Then, the age-neutrality of the questionnaires (i.e. to what extent younger and older adults having the same degree of personality pathology have the same probability of endorsing related items on the questionnaires) will be investigated. In case non-age-neutral items appear, the investigators will adjust these to obtain age-neutrality. This first research question will occur in the general population. After age neutrality has been demonstrated (possibly after adjustments of the questionnaires), the instrument will be applied in the clinical institutions to evaluate the rest of the research questions. In the clinical population, the construct validity of the questionnaires will be investigated. Construct validity will be evaluated by examining the factor structure of the questionnaires and correlations with other measures of psychopathology (e.g. symptoms of depression and anxiety measured by Brief Symptom Inventory or SCL-90-R). Furthermore, the clinical utility of the questionnaires will be investigated, by examining their ability to distinguish individuals with PDs from those without personality pathology. In addition to research on the psychometric qualities of the questionnaires, the investigators will also validate the AMPD and ICD-11 conceptualization of PDs in two criteria, in older patients by examining the incremental validity of criterion A, above and beyond criterion B. This means the investigators will determine the extent to which criterion A and criterion B can be distinguished from each other and whether they can be differentiated from each other (or in other words do not contain (too much) overlapping information).
2. The second central objective focuses on enhancing general knowledge about the structure and characteristics of PDs in older adults, by positioning PDs in a comprehensive framework of psychopathology, namely the HiTOP model (Hierarchical Taxonomy of Psychopathology) (Kotov et al., 2017). The HiTOP model is an empirical dimensional model that brings together PDs and other clinical disorders in a hierarchical structure, based on their shared transdiagnostic factors. To date, this model has not yet been investigated in older adults (Kotov et al., 2021). With this study, the proposed HiTOP structure will be tested in 65+, in order to gain more insight into the underlying transdiagnostic factors that characterize PDs in older adults, with the ultimate goal of better care and treatment tailored to the older patient.