Psychometric evaluation of the Adjustment Disorder New Module-20 (ADNM-20): A multi-study analysis

•Our findings demonstrate unidimensionality of adjustment disorder (AjD).•Total score of ADNM-20 should be used for capturing the construct of AjD.•ADNM-20 and ADNM-4 were reliable and valid to assess probable AjD among Hong Kong Chinese.•The prevalence of probable AjD was 20.5 % amid massive civil unrest in Hong Kong. The Adjustment Disorder New Module (ADNM) is a self-report instrument for assessing Adjustment disorder (AjD), but uncertainties remain in evaluating factor structure and psychometric properties of ADNM in previous studies. Three studies were conducted to examine the factor structure, psychometrics properties, and clinical utility of the 20-item version of ADNM (ADNM-20) and 4-item version (ADNM-4) among samples of Hong Kong Chinese (N = 1,415). Confirmatory factor analysis demonstrated good model fitness with a bifactor model. Statistical indices indicated unidimensionality of AjD. The model-based reliability showed that the total score of ADNM-20 should be used in scoring and interpretation for capturing the construct of AjD. ADNM-4 model demonstrated full invariance between women and men and partial invariance between age groups. Receiver operating characteristic analysis revealed a cutoff score of 10 for probable AjD. The prevalence of probable AjD was 20.5 % excluding cases with probable depression among a population-representative sample of Hong Kong Chinese amid civil unrest in Hong Kong in July 2019. Cutoff scores of ADNM-20 (49) and ADNM-4 (9) were established for clinically significant common psychiatric conditions, namely PTSD, depression, and anxiety. Both ADNM-20 and ADNM-4 were reliable and valid to assess probable AjD. Implications for clinical research and practice are discussed.