Hamilton Rating Scale for Anxiety: exploring validity with robust measures of classical theory parameters and a rating scale model in university students.

No research has assessed Hamilton Rating Scale for Anxiety (HRSA) psychometric properties in Ethiopian university students, using item response theory (IRT) and classical theory. This study aimed to assess psychometric properties of the English HRSA in Ethiopian students, using IRT and classical theory. University students (N = 370, age 21.44 ± 2.30 years) in Ethiopia participated in a cross-sectional study. Participants completed a self-reported measure of anxiety, a sociodemographics tool and interviewer-administered HRSA. Confirmatory factor analysis (CFA) favoured a one-factor structure because fit indices for the one-factor model; and two distinct two-factor models were similar, but high interfactor correlations violated discriminant validity criteria in two-factor models. This one-factor structure showed structural invariance as evidenced by multi-group CFA across gender groups. No ceiling/floor effects were seen for the HRSA total scores. Infit and outfit mean square values for all the items were within the acceptable range (0.6-1.4). Four threshold estimates (τi1, τi2, τi3 and τi4) for each item were ordered as expected. Differential item functions showed item-level measurement invariance for all the 14 HRSA items across gender for both uniform and non-uniform estimates. McDonald's ω and Cronbach's α for the HRSA tool were both 0.88. The convergent validity of the interviewer-administered HRSA with self-reported anxiety subscale of the 21-item Depression, Anxiety and Stress Scale was weak to moderate. The findings favour the validity of a one-factor structure of the HRSA with adequate item properties (classical and rating scale model), convergent validity, reliability and measurement invariance (structural and item level) across gender groups in Ethiopian university students.