Background: The Depression Anxiety Stress Scale 21 (DASS-21) is a mental health screening tool with conflicting studies regarding its factor structure. No studies have yet attempted to develop a computer adaptive test (CAT) version of it.
Objective: This study calibrated items for, and simulated, a DASS-21 CAT using a nonclinical sample.
Methods: An evaluation sample (n=580) was used to evaluate the DASS-21 scales via confirmatory factor analysis, Mokken analysis, and graded response modeling. A CAT was simulated with a validation sample (n=248) and a simulated sample (n=10,000) to confirm the generalizability of the model developed.
Results: A bifactor model, also known as the "quadripartite" model (1 general factor with 3 specific factors) in the context of the DASS-21, displayed good fit. All scales displayed acceptable fit with the graded response model. Simulation of 3 unidimensional (depression, anxiety, and stress) CATs resulted in an average 17% to 48% reduction in items administered when a reliability of 0.80 was acceptable.
Conclusions: This study clarifies previous conflicting findings regarding the DASS-21 factor structure and suggests that the quadripartite model for the DASS-21 items fits best. Item response theory modeling suggests that the items measure their respective constructs best between 0θ and 3θ (mild to moderate severity).
Keywords: CAT; DASS-21; anxiety; computer adaptive testing; depression; development; graded response model; mental health; model; psychological distress; reliability; screening tool; simulation; stress; tool.
©Jake Kraska, Karen Bell, Shane Costello. Originally published in the Journal of Medical Internet Research (https://www.jmir.org), 22.06.2023.