The present study provides unique data on depressive symptoms in a Brazilian sample of nonclinical adolescents. To the best of our knowledge, this study was the first to comprehensively examine the reliability, factor validity, and gender equivalence in diverse models of BDI-II, including bifactor models. Our analyses yielded several promising findings. In the EFA, the best model was the oblique two-factor one, with affective-cognitive and somatic dimensions. In the CFA, after checking measurement indicators of competing models, the unidimensional structure emerged as the best representative in our dataset. In fact, a robust general factor conspicuously emerged in tested bifactor models. In addition, we found evidence of measurement invariance across gender. Examination of bifactor models along with indicators of reliability, item variance and residuals provided fresh insights on the applicability of the BDI-II. A standardized and widely used instrument, such as the BDI-II, is pivotal for helping clinicians and researchers to understand the expression of depression in adolescents in different cultures. Further exploration of moderators that potentially affect the factor structure, such as culture, language, and urbanicity, among others, could support the utility of a measurement tool in different settings and contexts.
Regarding the EFA, our findings support a similar factor structure to the oblique two-factor solution (affective-cognitive and somatic) proposed by Beck et al. [8], Uslu et al. [30] and Huang & Chen [15]. Although these researchers also investigated nonclinical youths, the item loadings vary slightly across studies. Some items such as sadness, past failure, self-dislike, suicidal thoughts, and worthlessness have consistently loaded on the dominant cognitive-affective dimension. In contrast, other items such as loss of energy, changes in sleep patterns, changes in appetite, concentration difficulties, and tiredness have defined the somatic dimension. Importantly, previous clinical descriptions have reported somatic symptoms, such as loss of energy, changes in appetite and weight, fatigue, and insomnia as particularly common presentations among adolescents diagnosed with depression [4, 37]. While symptoms, such as concentration difficulties, worthlessness, guilt, and changes in sleep patterns could be viewed as early warning signs for MDD, symptoms like sadness, anhedonia and suicidal thoughts could indicate the severity of the depressive condition [38]. Although the affective-cognitive dimension in adolescents determined the core dominant data covariance, the somatic dimension could be a helpful marker of a potential depressive episode.
The oblique two-factor solution could not always be replicated across different samples. Some factor models failed to converge on the underlying structure; therefore, an alternative representation of two distinct dimensions should be considered. When highly correlated two-factor models were found in an EFA solution, this could indicate the presence of a general latent variable of depression partitioning for data distribution. Thus, the bifactor model has emerged as a sophisticated alternative for structural analysis of the BDI-II. However, so far, there are no clear guidelines or benchmarks for evaluating this measurement approach. To address this gap, we assessed bifactor CFA models by aligning fit criteria with bifactor indices reported in the literature.
Our CFA results revealed the unidimensional model as the best representation of observed data, considering substantive, statistical, and practical fit. The CFA is a theoretically grounded method. In our study, the two bifactor models showed a slightly better fit than simple structure models. The results of our parameter estimators for both bifactor models confirmed the existence of a strong general factor and indicated that most of the reliable variance in the total score was attributable to these factors. Regarding group factors, we observed several low loadings across all subgroups. For example, the indecisiveness, irritability, and concentration difficulties items clearly loaded on general depression factors and disappeared on specific factors.
Taken together, these results pointed to the possible existence of a factor over extraction and reinforced the BDI-II as a unidimensional scale. This is in line with the results of studies in adult samples [15]. In contrast, the scant studies available that conducted CFA with one, two- and three-factors, and second-order or bifactor models in adolescents revealed diverse findings. In clinical settings, among the two existing studies of CFA, one [16] concluded that none of the tested models met all adequacy-of-fit criteria, while another [17] supported a bifactor and a two-factor model as plausible solutions. To date, there are five studies of nonclinical samples. Byrne et al. [11] proposed a second-order factor model defined by three lower order factors comprising “negative attitude”, “performance difficulty”, and “somatic elements” and one higher order factor representing general depression. The best-fitting model, that of Wu and Huang [25], relies on three similar factors Byrne et al. model [14], but without the second-order factor structure. Lee et al. [19] also concluded that the BDI-II was best represented by the three-factor model. Osman et al. [18] found that all tested models showed good fit to the sample data, with superior fitness to the bifactor model (one general factor and two factors, i.e, somatic and cognitive-affective). After examining the loadings, they confirmed this model as a plausible alternative. Previously, Whisman et al. [39] had reported the Beck et al. [8] original oblique two-factor model (somatic-affective and cognitive), slightly modified, as the best fit model to older adolescents. It is important to note that, except for the Osman et al. study [18], the best CFA model was chosen only by the fit criterion. Thus, further CFA studies are needed to improve our understanding of the underlying construct of the BDI-II in nonclinical adolescents, considering further reliability indicators and bifactor statistics. The present study’s findings demonstrated that the one-factor model provided a better representation of the BDI-II to the data than more complex (i.e., bifactor) models that are becoming increasingly popular approaches for measuring depression psychopathology. However, a general depression factor does not invalidate the differentiation of specific depression factors as a distinct depression group factor, but it could prompt advancement in the comprehension of different etiologies and associated symptomatology.
Based on the MG-CFA, the unidimensional factor structure was invariant across gender. In other words, our findings suggested that the same BDI-II construct can be applied to both female and male adolescents. This accords with our original hypothesis and one study that also used a one-factor model for invariance analysis [24], but is somewhat at odds with others [16, 17, 25]. Although these studies found some degree of partial invariance, most of them concluded the effect of non-invariance on observed mean differences could be negligible. There are two possible reasons for the varied findings among the studies: the chosen baseline model and the characteristic of the samples. Measurement invariance is critically important when comparing groups. If measurement invariance cannot be established, then the finding of a between-group difference cannot be unambiguously interpreted [37]. In summary, our findings call attention to the need for further investigations, which could drive more specific care for female and male adolescents with depressive symptoms.
Limitations and future research
The findings should be interpreted considering the following limitations. We used a large and representative sample, and our results allow some generalization to the general adolescent population. However, it comprised only urban school-age adolescents and thus, the findings may need further validation in rural and dropped-out-of-school adolescents. The methods applied are well-established in the literature, suitable for data type, and are reproducible in other studies. Nevertheless, the examination of gender was based on a categorical variable (gender binary). Recent advances in measurement invariance analysis have enabled the test of invariance within a dimensional perspective [40]. Thus, further studies should investigate the invariance of the BDI-II across gender dimensions that may allow for more inclusive conclusions. Furthermore, the effect of puberty on the factor structure of the BDI-II was not examined in our data. The increasingly high level of lifetime prevalence of depression in females first arises after puberty and seems to be associated with hormonal changes [4]. Thus, further fine-grained gender-related invariance analyses across early and late adolescence may help to understand this gender gap. Lastly, given that Sao Paulo is a global city, the effect of race and ethnicity on the factor structure of depression is an important issue and should be addressed by future researchers.