Elsevier

Comprehensive Psychiatry

Volume 60, July 2015, Pages 170-181
Comprehensive Psychiatry

The Italian version of the Depression Anxiety Stress Scales-21: Factor structure and psychometric properties on community and clinical samples

https://doi.org/10.1016/j.comppsych.2015.04.005Get rights and content

Abstract

Objective

The Depression Anxiety Stress Scales-21 (DASS-21) is the short version of a self-report measure that was originally developed to provide maximum differentiation between depressive and anxious symptoms. Despite encouraging evidence, the factor structure and other features of the DASS-21 are yet to be firmly established.

Method

A community sample of 417 participants and two clinical groups (32 depressive patients and 25 anxious patients) completed the Italian version of the DASS-21 along with several measures of psychopathology.

Results

Confirmatory factor analyses suggested that the DASS-21 is a measure of general distress plus three additional orthogonal dimensions (anxiety, depression, and stress). The internal consistency and temporal stability of the measure were good; each DASS-21 scale correlated more strongly with a measure of a similar construct, demonstrating good convergent and divergent validity. Lastly, the DASS-21 demonstrated good criterion-oriented validity.

Conclusion

The validity of the Italian DASS-21 and its utility, both for community and clinical individuals, are supported.

Introduction

Depression and anxiety are highly comorbid conditions characterized by both shared and distinctive features. Their frequent co-occurrence, as well as the inability of traditional self-report measures to discriminate between them, is well known [1], [2], [3]. With regard to this, the Depression Anxiety Stress Scales (DASS) is a self-report questionnaire created with the initial aim of providing maximum differentiation between the core symptoms of depression and anxiety; the major development of the DASS was conducted on non-clinical samples [4], [5]. Items and scales were identified a priori on the basis of clinical consensus and were then empirically refined using factor analysis. A third factor emerged from the analysis of the items, which resulted in inadequate discrimination between anxiety and depression. It was labeled “stress” in that it was mainly characterized by irritability, nervous tension, difficulty relaxing, and agitation [4]. Thus, the final version of the DASS consisted of 42 items comprising three scales: (a) depression, assessing a lack of incentive, low self-esteem, and dysphoria; (b) anxiety, referring to somatic and subjective symptoms of anxiety, as well as acute responses of fear; (c) stress, evaluating irritability, impatience, tension, and persistent arousal [4]. Attempts to ascertain whether the stress scale measured a distinct syndrome or a general distress factor related to both depression and anxiety (likewise the Negative Affect postulated by the tripartite model, [6]) led to mixed results [7], [8], [9].

With the aim of developing a short form for use in research as well as in settings characterized by time constraint, Lovibond and Lovibond [5] selected seven representative items from the original DASS for each scale of the questionnaire; the identified items should have good factor loadings on the original measure and scores for each reduced scale should be very close to half of the respective full-scale score. This short measure was named the DASS-21. In the original manual, internal consistency data on a non-clinical sample are reported for the three scales (depression: α = .81; anxiety: α = .73; stress: α = .81), whereas neither factor analyses nor psychometric properties of the short scales are described [5].

Despite the potential importance of the DASS-21, few studies have examined the psychometric properties and factor structure of this measure in clinical [1], [10] and non-clinical [7], [11], [12], [13] adult samples. In general, such studies showed excellent1 internal consistency of the three scales of the DASS-21 (.80 < αs < .91) [7], [11], [12], [13], large convergent/divergent2 validity coefficients (rs ranging from .50 to .80, and from −.16 to −.48, respectively) [7], [12], [13], and good construct validity [11]. Medium to large correlations between the three DASS-21 dimensions (rs ranging from .46 to .75) [1], [10], [13] have been found. However, in several studies, correlations between stress and depression and stress and anxiety emerged as higher than those between depression and anxiety factors [1], [10].

Overall, the results from confirmative factor analyses (CFAs) supported the original three-factor structure [1], [7], [10], [11], [13], and only a few alternative solutions have been reported [7], [12]. For instance, Clara et al. [10] investigated the internal structure of the DASS through eight CFAs in a sample of patients with mood disorders: the original 42-item DASS [4]; the revised three-factor structure of the 42-item DASS proposed by Brown et al. [14], where two items were allowed to load on both the stress and anxiety factors; the original DASS-21 [4]; a version of the DASS-21 comprising the 21 items of the 42-item DASS that were excluded from the original DASS-21; and four different sub-sets of the DASS items, previously identified by Lovibond and Lovibond [4] and representing theoretically defined syndromes of anxiety, depression, and stress (i.e. “tripartite models”) [10]. The results highlighted that the original DASS-21 model showed better fit indices than the two DASS-42 models and the other DASS-21.

Henry and Crawford [7] observed that a four-factor (quadripartite) model, consisting of the three depression, anxiety, and stress dimensions plus a general distress factor, represented the optimal fit of all the structures they tested. Thus, their findings sustain the hypothesis of the three factors as independent but acknowledge the existence of a more general factor that shares variance with the three of them. On the other hand, Osman et al. [12] conducted exploratory and confirmatory item bifactor analyses on the DASS-21 in order to investigate the extent to which each item is associated with a domain-specific dimension (i.e., the three DASS-21 factors) or a general dimension; they concluded that the DASS-21 may measure a general distress dimension rather than independent dimensions of depression, anxiety, and stress.

Partial support for the three-factor structure and good psychometric properties of the DASS-21 also came from studies validating foreign versions of the questionnaire [15], [16], [17], [18]. For instance, in a recent study, Oei et al. [19] examined the cross-cultural validity of the DASS-21 among six Asian community samples (i.e., Malaysian, Indonesian, Singaporean, Sri Lankan, Taiwanese, and Thai). Three factors emerged from the exploratory factor analysis (EFA), and three items were removed from the stress scale due to loadings on more than one factor. Three different solutions were then compared by means of CFA: three-factor DASS-21, three-factor DASS-18, and one-factor DASS-18. The three-factor DASS-18 resulted in the best solution; it also showed good-excellent internal consistency values (.70 < αs < .86) and satisfactory convergent validity (.50 < rs < .60) with the Beck Depression Inventory-Second Edition (BDI-II) [20], the Beck Anxiety Inventory (BAI) [21], and the Positive and Negative Affect Schedule, Negative Affect subscale (PANAS-NA) [22].

The use of the DASS-21 in research and clinical practice may hold great promise: the questionnaire is in the public domain; its widespread use is well documented; its relatively short format guarantees a good ease of use in different settings since it is not a time-consuming self-report measure; lastly, it has been shown to be responsive to change in clinical status [23], [24]. Furthermore, the DASS-21 has a comparable or even clearer latent structure than the original version [1], [7], [10]; it is as reliable and discriminative as the DASS [1]; its factorial structure is similar in both clinical and non-clinical samples [1], [7], [10], [11], [13]; and its psychometric properties and factor structure have been found to converge across different cultures [16], [18], [19], [25].

Nonetheless, an Italian validation of the DASS-21 is not available to date. Although Severino and Haynes [26] previously developed an Italian version of the original DASS, at least four limitations currently prevent its use in the Italian clinical and research contexts. First, the items are not written in a good and sound Italian language. Second, the participants were a particular sub-sample of the Italian population, that is, Italian adults who had emigrated to Australia. Third, the age of the sample (55–90) was not typical of questionnaire validation studies. Lastly, no clinical sample was considered in the study. Therefore, a more readable version of the questionnaire, administered to a more representative Italian sample as well as to clinical individuals, is needed and could provide more reliable data.

Furthermore, despite the above-mentioned potentialities of the DASS-21, a number of issues still have to be further explored. First, no complete agreement in regard to the factor structure of the DASS-21 has been achieved (one-factor vs. three-factor vs. bifactor structure; see previously mentioned studies); second, data about temporal stability are lacking; third, a scarce (and inconsistent) number of findings regarding gender differences have been reported [11], [25], [27]; likewise, the relationships between the DASS-21 and age and education in adult samples have not been investigated. Fourth, it is also important to note that, whereas the convergent/divergent validity of the DASS, as well as that of the DASS-21, has mostly been investigated for anxiety and depression scales, only one study has adopted specific measures of stress to study the convergent/divergent validity of this measure [12]. Lastly, only a few studies tested the psychometric properties of the DASS-21 on clinical samples that were composed of depressive and anxious patients [1], [10], [15], [16], [25].

In consideration of the potential utility of the DASS-21, as well as its current unavailability in Italy, the main aim of the present study was to provide data on the factorial structure and psychometric properties of the Italian version of the questionnaire by administering it both to community and clinical individuals.

In the first place, the current study aimed to explore the factor structure of the Italian DASS-21 by performing three CFAs that tested three different models: a unidimensional model, a three-factor oblique model, and a bifactor model. Furthermore, we sought to explore the internal consistency, temporal stability, and construct validity of the Italian DASS-21 in both clinical and non-clinical samples, as well as criterion validity as concurrent validity, i.e., whether DASS-21 subscale scores can adequately discriminate between known groups such as non-clinical participants and depressed and anxious patients. Moreover, we addressed novel issues scarcely investigated in previous studies. First, we analyzed the associations between the three original DASS-21 scale scores and age and education in our adult sample (>18 years), speculating that we would find small correlations between these variables. Furthermore, since few statistics on gender differences have been reported in the literature, we aimed to further investigate them in the present sample. Overall, the results from the few studies taking into account this issue reported that females obtain higher scores than males in the DASS-21 scales, but different patterns have been found [11], [25], [27]. Lastly, since we did not have sufficient data to formulate a clear hypothesis on clinical participants with respect to the DASS-21 stress scale, we speculated that scores on this scale should be higher in all patients compared to normal controls, with few differences among patients, because the scale measures a general state of tension and irritability.

Section snippets

Participants and procedure

Four hundred and seventeen individuals (42.9% male), who reside in 10 different middle-sized communities in northern and central Italy and who had responded to advertisements requesting potential volunteers for psychological studies, entered the study. All participants were Caucasian. The mean age of the sample was 36.39 (SD = 13.71; range = 18–80) and the mean years of education was 14.18 (SD = 3.45; range = 5–23). Marital status was 48.8% single, 47.4% married or cohabitating, 2.2% separated or

Factor structure

In order to identify the best factor structure of the Italian DASS-21 in the community sample and following the recommendations by Reise et al. [45], we conducted three different CFAs that tested three respective models: A) a unidimensional model (all 21 items loading on a single factor); B) a three-factor oblique model (the original DASS-21 model) [4]; and C) a bifactor model in which each of the 21 items is constrained to load on a general factor and on one out of the three (uncorrelated)

Discussion

The present study aimed to evaluate the factor structure and psychometric properties of the Italian DASS-21 on a large community sample, as well as its utility in discriminating between depressive and anxious patients. With respect to the internal structure of the questionnaire, results from the series of CFAs suggested that, despite the original three-factor oblique model [4] showing good fit indices, the best factor solution is a bifactor model. This was further supported by the evaluation of

Acknowledgment

The authors would like to acknowledge Prof. Peter F. Lovibond for providing a copy of the DASS-21 and for granting permission for it to be used in the present study.

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