Rasch model analysis of the Depression, Anxiety and Stress Scales (DASS)

Tracey L Shea,Alan Tennant,Julie F Pallant

doi:10.1186/1471-244x-9-21

Abstract

BackgroundThere is a growing awareness of the need for easily administered, psychometrically sound screening tools to identify individuals with elevated levels of psychological distress. Although support has been found for the psychometric properties of the Depression, Anxiety and Stress Scales (DASS) using classical test theory approaches it has not been subjected to Rasch analysis. The aim of this study was to use Rasch analysis to assess the psychometric properties of the DASS-21 scales, using two different administration modes.MethodsThe 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.ResultsTo 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.ConclusionThe 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.

Highlights

There is a growing awareness of the need for administered, psychometrically sound screening tools to identify individuals with elevated levels of psychological distress
The sample consisted of a total of 420 respondents with 210 (50%) completing the pencil and paper version of the DASS-21 and 210 (50%) completing the web-based version of the scale
Replication in better targeted samples, with higher levels of anxiety and depression, would further support the robustness of the current findings. This was the first study to undertake a rigorous examination of the psychometric properties of the DASS-21 using Rasch analysis and to assess item bias by mode of administration

Summary

Introduction

There is a growing awareness of the need for administered, psychometrically sound screening tools to identify individuals with elevated levels of psychological distress. The aim of this study was to use Rasch analysis to assess the psychometric properties of the DASS21 scales, using two different administration modes. According to the World Health Organisation (WHO) mental illness is prevalent, in all strata across all countries and societies [1]. Disorders such as schizophrenia, bipolar disorder, depression and anxiety and dementia related disorders are some of the main reasons individuals live with disability. BMC Psychiatry 2009, 9:21 http://www.biomedcentral.com/1471-244X/9/21 result in a substantial reduction in perceived quality of life This may manifest as restricted participation in the workplace, reduction in general health and dissatisfaction in family or social life [4,5,6]. A study by Suominen, Henrikkson, Suokas et al [10] found that 38% of suicide attempters had been reported to have major depressive disorder while 75% were diagnosed with a depressive syndrome (e.g. major depression, depressive disorder not otherwise specified)

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