Validation of the 21-item Depression, Anxiety, and Stress Scales (DASS-21) in individuals with autism spectrum disorder

Highlights

• The psychometric properties of the DASS-21 were examined in individuals with ASD.

• The DASS-21 demonstrated high internal consistency and item-total correlations.

• The DASS-21 showed adequate convergent validity and acceptable factorial validity.

• The original 3-factor structure of the DASS-21 was supported in this study.

• Self-reports of depression by adults with ASD showed higher severity than clinician reported ratings of the same person.

Abstract

The purpose of the study was to examine the internal consistency and validity of the 21-item Depression Anxiety Stress Scale (DASS-21) in individuals with Autism Spectrum Disorder (ASD) and without intellectual disability (IQ >= 70). Participants (NN = 123) were consecutively recruited from the Brain and Mind Centre in New South Wales, Australia. Internal consistency was determined using Cronbach's alpha. Item-total correlations were evaluated by Pearson's product-moment correlation coefficient. The convergent validity of the DASS-21 was examined by measuring its associations with quality of life and other measures of depression and anxiety. Factorial validity was assessed using confirmatory factor analysis. The DASS-21 demonstrated good internal consistency, adequate convergent validity, and all items exhibited satisfactory item-total correlations. Considering fit indices and factor loadings, the confirmatory factor analysis results provided support for the original 3-factor oblique model consisting of depression, anxiety, and stress factors. The model fit could be further improved with some modifications. Overall, the results indicate that the DASS-21 is a viable self-report screening measure for depression, anxiety, and stress in individuals with ASD and without intellectual disability.

Introduction

Autism spectrum disorder (ASD) is the collective term for neurodevelopmental disorders characterized by impaired social interaction and communication, as well as a restricted range of activities and interests (American Psychiatric Association, 2013). Co-occurring depression and anxiety are common in this population (Eaves and Ho, 2008). The reported prevalence rates for depression disorders in adults with ASD range from 38% to 70%, while the reported prevalence rates for anxiety disorders range from 50% to 65% (Hofvander et al., 2009; Lugnegard et al., 2011). Their presence has been found to exacerbate the core features of ASD (Rai et al., 2018). Despite the high prevalence, diagnosis, and treatment of these co-occurring conditions in ASD, they are often under-recognized and under-treated (Mazzone et al., 2012).

Co-occurring depression is associated with impaired social communication, maladaptive behaviours, lower adaptive functioning and a higher risk of suicide in individuals with ASD (Cassidy et al., 2014; Stewart et al., 2006). Cassidy et al. (2014) found that 66% of individuals with ASD reported suicidal ideations, and 35% reported past planned or attempted suicides. There is also considerable overlap between the symptoms of ASD and depression, such as social withdrawal, appetite, and sleep disturbance, which can also result from difficulties related to autism (Stewart et al., 2006). Consequently, it has been suggested that clinicians and researchers may overestimate the severity of depressive symptoms in individuals with ASD when using traditional depression measures developed for those without ASD (Cassidy et al., 2018).In people with ASD, higher levels of anxiety are associated with increased functional impairment (McKnight et al., 2016), theory of mind impairment (Ozsivadjian and Knott, 2011), repetitive behaviours (Lidstone et al., 2014), and insomnia symptoms (Richdale et al., 2014). The severity of anxiety symptoms in individuals with ASD may also be challenging to diagnose due to the overlapping symptoms (e.g., social avoidance and repetitive behaviour) of anxiety and ASD (Hollocks et al., 2019; Kerns and Kendall, 2012). As a result, the reliability and validity of traditional anxiety measures in individuals with ASD have been questioned (Vasa et al., 2018).

Given that co-occurring depression and anxiety can profoundly affect individuals with ASD, there is a crucial need to identify reliable and valid measures of these constructs in this cohort. However, there has been limited research identifying reliable and valid self-report measures (Cassidy et al., 2018; Rodgers et al., 2016). Many researchers have highlighted the need to validate existing tools used in the general population before developing specific instruments for ASD, partly to ensure people have access to mainstream assessment and treatment services (Cassidy et al., 2018; Rodgers et al., 2016).

As a self-report questionnaire for measuring depression, anxiety, and stress, the 21-item Depression, Anxiety, and Stress Scale (DASS-21; Lovibond and Lovibond, 1995) has been used extensively in a wide range of research and clinical settings, in part due to its ability to adequately differentiate between specific anxiety and depression clusters of symptoms (Antony et al., 1998; Henry and Crawford, 2005; Lovibond and Lovibond, 1995). Unlike the structured or semi-structured interviews that can take 1 to 4 h of administration, the DASS can be administered quickly by clinicians and as a self-report instrument. The DASS is designed to measure the dimensions of depression, anxiety, and stress that vary along a continuum of severity. Therefore, the DASS cannot be used on its own to determine the presence or absence of depression or anxiety and should not replace a clinical interview. However, high scores on the DASS alerts clinicians to identify patients who are at high risk of being affected by depression or anxiety, indicating the need for further diagnostic assessment (Lovibond and Lovibond, 1995). In addition to the use of DASS as a screening tool, the DASS can also be used to assess the patient's response to treatment (Ronk et al., 2013).

In comparison to the DASS, most traditional self-report scales (e.g., Hamilton Rating Scales for Anxiety and Depression; Hamilton, 1959, 1960) may not distinguish well between anxiety and depression, as these scales predominantly measure the common factor of negative affectivity (Moras et al., 1992; Watson and Clark, 1984). Several studies have evaluated the factor structure of the DASS-21 using confirmatory factor analysis in both clinical (e.g., Clara et al., 2001) and nonclinical samples (e.g., Henry and Crawford, 2005). Previous studies have reported adequate internal consistency of the DASS-21 (α = 0.88–0.92 for depression, 0.79–0.83 for anxiety, 0.84–0.86 for stress and 0.93 for total) in adults with ASD (Cage et al., 2018; Maddox and White, 2015; Nah et al., 2018). There was, however, no report of its convergent and factorial validity, which is required to determine its utility for this population (Cassidy et al., 2018). In Australia, the 21-item version of the DASS (DASS-21) is also used nationally for reporting on publicly funded mental-health care plans for psychological therapy, owing to its excellent psychometric properties and free public use (Pirkis et al., 2011). Given that the scale has not been previously validated in ASD populations, this has led to limited use and subsequent barriers for accessing subsidized mental health care for the ASD population. It is, therefore, critical that its psychometric properties are evaluated in neurodiverse populations to encourage its use and appropriate access, assessment, and monitoring for publicly funded mental health programs.

The present study aimed to evaluate the psychometric properties of the DASS-21 in individuals with ASD and without intellectual disability. More specifically, we assessed the instrument's internal consistency, item-total correlations, convergent validity, and factorial validity. It was hypothesized that in adults diagnosed with ASD, all three scales of the DASS-21 would show an adequate level of internal consistency and correlate significantly with other instruments of depression and anxiety, such as Hamilton Rating Scale for Depression (HAM-D; Williams, 1988) and Liebowitz Social Anxiety Scale Self-Report (LSAS-SR; Fresco et al., 2001; Liebowitz, 1987). Further, it is expected that all three DASS-21 scales would correlate negatively with quality of life (QoL) measured by the 12-Item Short Form health survey (SF-12; Ware et al., 1996). Finally, we predicted that all items on the DASS-21 would be a relevant measure of their intended constructs.