Validation of the depression anxiety stress scales (DASS) 21 as a screening instrument for depression and anxiety in a rural community-based cohort of northern Vietnamese women

Depression and anxiety are the common non-psychotic mental disorders experienced most frequently by women living in resource-constrained low and lower-middle income countries [1, 2]. Early detection of these problems in primary health care is essential to identifying women who might be offered targeted treatments and therefore to improving prognosis among them and reducing disability in the community [3]. As the competing health priorities of infectious illness and malnutrition are diminishing in these settings, awareness of mental health is growing. There is an increasing need for screening tools, which primary health care staff can use, to identify people experiencing common mental disorders in the community.

The relationship between depression and anxiety has been of longstanding interest to clinicians and researchers. Clark and Watson [4] proposed a tripartite model of anxiety and depression. This model suggests that both conditions share several symptoms of elevated negative effect (e.g. distress and irritability). Depression is characterised by low levels of positive effect including experiences of happiness, confidence, and enthusiasm, while physiological hyperarousal is unique to anxiety. Even though depression and anxiety are conceptually distinct, there is substantial overlap between the two states that makes them difficult to distinguish in screening.

The Depression Anxiety and Stress Scales (DASS, [5]) is a widely used screening tool to assess symptoms of depression, anxiety, and stress in community settings. This instrument comprises three sub-scales: (1) the Depression sub-scale which measures hopelessness, low self-esteem, and low positive affect; (2) the Anxiety scale which assesses autonomic arousal, musculo-skeletal symptoms, situational anxiety and subjective experience of anxious arousal; and (3) the Stress scale which assesses tension, agitation, and negative affect. There are two forms of the DASS, the full 42-item and the short 21-item versions. Both assess the same domains.

There is evidence of the validity of the DASS for the use in both clinical and community settings in English-speaking countries including Australia [6, 7], the United States of America [8], Canada [9], and England [10]. This tool has also been translated and validated in other languages including Chinese [11], Malay [12], Italian [13], and Spanish [14]. Both English and non-English versions have high internal consistency (Cronbach’s alpha scores of > 0.7). Previous investigations in English-speaking and non-English-speaking countries have found significant correlations between DASS scores and other measures including the Beck Anxiety and Beck Depression Scales (correlation coefficients, r, ranged from 0.58 to 0.78, [6]), the Positive and Negative Affect Scale (r = 0.69, [10]), and Symptom Checklist-90-R (r ranged from 0.57 to 0.84, [14]). However, there has not yet been a validation study of the DASS21 against a clinical diagnostic test to propose and verify cut-off scores to detect common mental disorders.

There is only a small set of psychometric instruments to detect symptoms of common mental disorders that have been validated for use in Vietnam. Our team has established the psychometric properties of Zung’s Self-rated Anxiety Scale, the Edinburgh Postnatal Depression Scale, and General Health Questionnaire 12 items for screening for common mental disorders including depression and anxiety during pregnancy and in the postpartum year [15] and the Self Reporting Questionnaire-20 items to establish psychiatric caseness in adult women [16]. The Depression Anxiety and Stress Scale is a brief screening instrument, which is of particular value because it can assess multiple domains and is psychometrically sound in Anglophone and no-Anglophone settings, but its comprehensibility and psychometric properties in resource-constrained countries have not yet been established [8].

The aim of this study was to establish the comprehensibility and psychometric properties including internal reliability and criterion validity of the Depression, Anxiety and Stress Scale as a screening instrument for depression and / or anxiety in women with young children living in rural northern Vietnam.

The study used the gold-standard design for scale validation of comparing the responses to the instrument with an independently administered diagnostic interview.

This study used gold standard validation methods in a systematically recruited representative sample of women. It used standard analyses of internal reliability of psychometric instruments and means of establishing cut-off scores to detect clinically significant symptoms of depression and anxiety. We acknowledge the limitation that our sample was limited to women who had children of the same age. We used a sampling method which allowed us to recruit a representative sample of women with young children of Ha Nam, a typical rural northern province in Vietnam. The social-demographic characteristics of our sample are identical to that of rural women with young children in the North of Vietnam in The UNICEF Multiple Indicator Cluster Survey 2006 [22]. Therefore we believe that the data can be generalised with confidence to rural northern Vietnamese women with young children.

The results of EFA, analyses of the median scores of the three sub-scales by diagnostic groups and ROC analyses are consistent in indicating that in this setting, there is only one dimension of psychological functioning underlying the 21 items of the DASS21-Vietnam Validation (DASS21-V). None of the subscales was able to distinguish women experiencing depression from those with an anxiety disorder. These findings, are similar to our previous validations of other psychometric instruments in this setting [15], and suggest that while screening tools are able to detect clinically significant psychological states, they are not able to distinguish which state an individual woman is experiencing. It is possible that the symptoms which distinguish between depression and anxiety in Vietnamese women were absent in the screening tools and this warrants further investigation in future studies.

The other interpretation is that non-psychotic psychological morbidity is more accurately conceptualised in this setting as a continuum, rather than a distinct series of separate conditions. The term “common mental disorders” which refers to depression and anxiety is widely used in existing research to indicate that these are not readily distinguishable from each other in resource-constrained settings [1, 2]. We have shown that in rural Vietnam there are the same risk factors for depressive and anxious states: intimate partner violence, low household wealth and coincidental adverse life events which are common among women in resource-constrained countries [17]. At community level therefore it might not be necessary to distinguish between these states as interventions such as universal psycho-educational programs or targeted supportive therapy to address these risks will be similar.

Consistent with previous studies [15, 23], this study shows that psychological symptom screening tools have lower cut-offs in Vietnam compared with those in high-income settings. DASS21-D and DASS21-S which include only psychological items have optimal cut-offs in this study at the borderline of normal and mild levels of symptoms in the Australian classification (Table 1). DASS21-A in which three of the seven items are somatic symptoms has a cut-off score to detect anxiety in this study falling in the range of the moderate level in the Australian classification. The reason may be that women with depression and anxiety tend to endorse more somatic symptoms than negative emotions.

These data demonstrate that both the combination of DASS21-D subscale and DASS21-A subscale and the combination of all three sub-scales generate a sensitive tool to screen for common mental disorders among women with young children in this setting. We suggested the combination of 21 items of DASS21 for primary health care because it has higher sensitivity and specificity than either any of the single sub-scales or combinations of two sub-scales. The optimal cut-off score of this tool is equal to or more than 34 which yields optimal sensitivity (79.1%) and specificity (77.0%) to detect common mental disorders including depression and anxiety. Using the full scale with 42 items may have different results. However, it would increase the burden and there would be no difference in treatment.

In summary, our data indicate that DASS21-V as a single scale has good internal reliability and is sensitive to detect common mental disorders in rural northern Vietnamese women with young children. Using the sub-scales to distinguish between depression and anxiety is not however appropriate for this setting. Overall, the DASS 21-V is a comprehensible and psychometrically sound tool which can be used in primary health care, community interventions, or as a screening tool at clinical settings in rural Viet Nam.