Can personality disorder be accurately assessed in older age? A differential item functioning analysis of ICD-11 inventories

Objectives: The contested categorical personality disorder (PD) criteria are not well suited to inform PD diagnoses in older adults. Yet, the classification of PDs is undergoing a critical transition phase with a paradigm shift to a dimensional approach for diagnosing PDs. No special attention was given to the expression of PDs in older age when the dimensional ICD-11 model was developed. Given that PDs are highly prevalent in older adults, there is an urgent need to examine if ICD-11 related instruments are able to adequately assess for PDs in older adults. Methods: The age-neutrality of ICD-11 measures was examined in a sample of 208 Dutch community-dwelling adults (N = 208, M age = 54.96, SD = 21.65), matched on sex into 104 younger (age range 18–64) and 104 older (age range 65–93) adults. An instrument is considered not to be age-neutral if a collective large level of differential item functioning (DIF) exists in a group of items of an instrument (i.e., 25% or more with DIF). We therefore set out to detect possible DIF in the following ICD-11 self-report measures: the Standardized Assessment of Severity of Personality Disorder (SASPD), the Personality Inventory for ICD-11 (PiCD), and the Borderline Pattern Scale (BPS). Results: DIF analyses using a non-parametric odds ratio approach demonstrated that SASPD, PiCD, and BPS were age-neutral with less than 25% of items showing DIF. Yet, impact of DIF at scale level, examined by way of differential test functioning (DTF), indicated a DTF effect on the SASPD total score. Conclusions: These results of age-neutrality of the PiCD and BPS are promising for measuring ICD-11 traits and the borderline pattern. Yet, the age-neutral measurement of PD severity requires further research. With a rapidly aging population, its accurate assessment across the entire adult life span, including older age, is a prerequisite for an adequate detection of PDs.