Rasch model analysis of the Depression, Anxiety and Stress Scales
(DASS)
BMC Psychiatry, 05/15/09
Shea TL et al. - The results provide support for the measurement properties, internal consistency reliability, and unidimensionality of three slightly modified DASS-21 scales, across two different administration methods. The further use of Rasch analysis on the DASS-21 in larger and broader samples is recommended to confirm the findings of the current study.
Methods- The DASS-21 was administered to 420 participants with half the sample responding to a web-based version and the other half completing a traditional pencil-and-paper version.
- Conformity of DASS-21 scales to a Rasch partial credit model was assessed using the RUMM2020 software.
- To achieve adequate model fit it was necessary to remove one item from each of the DASS-21 subscales.
- The reduced scales showed adequate internal consistency reliability, unidimensionality and freedom from differential item functioning for sex, age and mode of administration.
- Analysis of all DASS-21 items combined did not support its use as a measure of general psychological distress.
- A scale combining the anxiety and stress items showed satisfactory fit to the Rasch model after removal of three items
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