Assessing psychosocial maturity to diagnose severe personality development disorders in young adult males adjudicated of serious criminal offences: a psychometric validation study of a new instrument

BACKGROUND: Psychosocial maturity is one of the key factors for understanding the course of criminal offences in juveniles and young adults. Until recently, forensic-psychiatric assessments to diagnose a severe disorder of personality development remained mostly unguided because validated instruments were not available. A new tool, the Young Adult Personality Development (YAPD) instrument, was introduced in 2021 and consists of three dimensions related to psychosocial maturity: YAPD environmental, YAPD pathology and YAPD developmental tasks failure. The current study tested the reliability (internal consistency, interrater reliability) and concurrent validity of these dimensions. METHODS: We analysed files of a consecutive sample of young adults in the Canton of Zurich (2007 to 2020, n = 234, mean age: 21.33 years, SD: 1.74 years), who were either assigned to specialised institutional treatment for young adults (Swiss Penal Code [SPC] Article 61) or outpatient treatment (SPC Article 63). Intraclass correlation coefficient (ICC) agreements were used to analyse interrater reliability of YAPD dimensions across three independent raters. In the absence of a gold standard, we analysed concurrent validity by measuring the associations of the YAPD dimensions with expert opinion and sample status (judicial decisions on measures) using multiple logistic regressions. RESULTS: Expert-rated personality development disorder was found to be highly prevalent in both samples. The YAPD dimensions showed adequate-to-good interrater reliability (ICC: 0.74–0.92). In logistic regression models, YAPD developmental tasks failure was related to diagnoses of severe development disorder and juridical decision on a measure for young adults according to SPC Art. 61. YAPD environmental was related to the diagnosis of a severe development disorder. YAPD pathology was found to be unrelated to the diagnosis of severe personality development disorder. CONCLUSIONS: Our findings support the YAPD developmental tasks failure dimension and to a lesser degree the YAPD environmental dimension as valid dimensions to diagnose severe personality development disorder. Structured assessment instruments such as the YAPD may further improve diagnostic decision-making in forensic psychiatry and psychology.