Research reportPsychometric properties of the Depression Anxiety and Stress Scale-21 in older primary care patients☆
Introduction
Lovibond and Lovibond (1995a) developed a single measure to assess the core symptoms of depression and anxiety while maximizing discriminant validity between these constructs. Using an empirically-driven iterative process, they identified a third factor, which they labeled stress. Their research resulted in the Depression Anxiety Stress Scales (DASS), which consists of 42 items comprising three scales of 14 items. Items refer to the past week; and scores range from 0, “Did not apply to me at all”, to 4, “Applied to me very much, or most of the time”. The Depression scale measures hopelessness, low self-esteem, and low positive affect. The Anxiety scale assesses autonomic arousal, physiological hyperarousal, and the subjective feeling of fear. The Stress scale items measure tension, agitation, and negative affect. The scales are considered to approximate facets of diagnostic categories, as follows: Depression scale for mood disorders, Anxiety scale for panic disorder, and Stress scale for generalized anxiety disorder (GAD; Brown et al., 1997). With the exception of GAD and obsessive–compulsive disorder, the Anxiety scale also corresponds reasonably closely to the symptomatology of other anxiety disorders. Subsequent research established a 21-item version of the DASS (DASS-21) with seven items per scale (Antony et al., 1998).
Numerous studies have found favorable psychometric properties of the DASS in adults with anxiety and/or mood disorders (Antony et al., 1998, Brown et al., 1997, Clara et al., 2001), Spanish-speaking patients (Daza et al., 2002), and community-dwelling adults (Crawford and Henry, 2003). All studies have demonstrated excellent internal consistency of the DASS scales in both the 42- and 21-item (DASS-21) versions: Depression (range = .91 to .97); Anxiety (range = .81 to .92); and Stress (range = .88 to .95). A three-factor solution reflecting the three scales has been found consistently across samples and factor-analytic techniques with only minor variations. Inter-scale correlations range as follows: Depression–Anxiety (.45–.71; .50 or below in all English-speaking samples (Antony et al., 1998, Brown et al., 1997, Clara et al., 2001), Anxiety–Stress (.65–.73), and Depression–Stress (.57–.79).
Despite encouraging psychometric data with the DASS in younger adults, the measure remains untested in older adults. Given the high prevalence of anxiety, depression, and comorbid anxiety–depression in older adults and the need for briefer instruments that efficiently evaluate these symptoms in older patients, the DASS may be a particularly useful measure in this population.
GAD is the most prevalent of the pervasive anxiety disorders in later life in both community and primary care samples (Blazer et al., 1991, Beekman et al., 1998, Wittchen et al., 2001, Tolin et al., 2005) but probably one of the most difficult to diagnose. Depression is also highly prevalent in older adults and frequently co-occurs with GAD (Beekman et al., 2000). Differentiating GAD and depression is particularly difficult in older adults given that the relationship between depression and anxiety is further obfuscated by loss of function and increased somatic presentation (Lenze et al., 2001, Lenze et al., 2005). Some researchers refer to this state as “depletion” as opposed to pure “depression” (Schoevers et al., 2005). A better understanding of these issues is clearly needed in the assessment of older adults. With respect to the DASS, the Anxiety scale contains some somatic items that could be experienced by older adults for reasons unrelated to emotion (e.g., breathing difficulty in the absence of exertion). In contrast, the DASS-D does not contain somatic items, thus limiting the likelihood of artificial score inflation observed in other measures of depression (Taylor et al., 2005). Given these considerations of developmental changes, psychometric results from younger adults cannot automatically be generalized to the measurement of anxiety and depression in later life (Beck and Stanley, 2001).
For this population, a measure that efficiently assesses and differentiates anxiety and depression would be most useful, given the need to reduce patient burden. Furthermore, older adults usually present to primary care settings, where few resources are available to support intensive, clinician-administered differential diagnostic procedures. As such, the DASS may be particularly useful for older adults, although its psychometric properties need to be examined in this population.
This study examined the psychometric properties of the DASS-21 in a population of older adults seeking help for worry in a primary care setting. Investigation of the psychometric properties included factor structure, internal consistency, and convergent and discriminative validity. We hypothesized that: a) a three-factor solution would better fit the data than other solutions; b) the DASS would demonstrate good internal consistency across all scales; c) the DASS would demonstrate good convergent validity in this sample; d) the DASS scales would differentiate different diagnostic groups; and e) the DASS scales would predict the presence vs. absence of GAD and mood disorders as well as other symptom-specific scales.
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Participants
Participants were 222 primary care patients 60 years of age or older referred for evaluation in the context of an ongoing randomized clinical trial of cognitive behavioral therapy for late-life worry and GAD in Houston, Texas. Potential participants were identified via primary care physician referrals, advertisements/educational brochures in primary care clinics, and/or letters sent to random samples of clinic patients 60 years or older. Of 968 primary care patients referred to the study, 858
Sample characteristics and descriptive statistics of measures
Sample characteristics, means, and standard deviations for all measures used in this study are depicted in Table 1. Consistent with convention, all DASS-21 raw scores were doubled to facilitate comparison with previous research and norms established using the DASS-42. Principal diagnoses were GAD (n = 134, 60.4%), MDD (n = 24, 10.8%), social phobia (n = 5, 2.3%), anxiety NOS (n = 5, 2.3%), adjustment disorder (n = 4, 1.8%), pain disorder (n = 4, 1.8%), panic/agoraphobia (n = 3, 1.4%), dysthymia (n = 2, 0.9%),
Discussion
This study is the first to investigate the psychometric properties of the DASS-21 in older adults. Analyses examined the factor structure, internal consistency, convergent and discriminative validity, and diagnostic utility of the DASS-21. CFA of the DASS-21 indicated that a three-factor solution best fit the data. This is consistent with findings from populations of adult anxiety-disordered patients (Antony et al., 1998), adult Spanish patients (Daza et al., 2002), and adult mood-disordered
Role of funding source
This research was supported by Grant 53932 from the National Institute of Mental Health to the last author. The NIMH had no further role in study design, data collection, data analysis, interpretation, writing of the manuscript, or in the decision to submit the paper for publication.
Conflict of interest
None of the author's have conflicts of interest.
Acknowledgments
The authors wish to express their appreciation to Paula Wagner, Jessica Calleo, Antje Dietel, and Sonora Hudson for their help in preparing this manuscript.
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Portions of this work were presented at the 2006 convention for the Association for Behavioral and Cognitive Therapies, November, Chicago.