Abstract
Two meta-analyses examined the factor structure of the Beck Depression Inventory–II (BDI-II). Study 1, which meta-analyzed 51 studies comprising 62 samples (N = 20,475) providing pattern matrices, determined that the two-factor solution comprising Cognitive and Somatic-Affective factors was supported for the full sample. The two-factor solution was also supported for subgroups of studies. As the factor structure varied somewhat between subgroups of studies, the strength of relationships between scale items and their underlying depressive symptoms varied. Hence, comparisons of mean BDI-II scores across subgroups can be misleading. Study 2 meta-analyzed 13 studies consisting of 16 samples (N = 5,128) providing covariance matrices among the 21 BDI-II items. The two-factor solution was again supported in Study 2. Nevertheless, the existence of a general depression factor was supported by the good fit of the one-factor model.
Keywords
Depression can seriously impair an individual’s functioning and is frequently associated with other mental disorders (Ohayon & Schatzberg, 2010) and compromised physical health (Shulz, Beach, Ives, Martire, Ariyo, & Kop, 2000). The Beck Depression Inventory–II (BDI-II) is a popular scale to assess the presence and severity of depression for adolescents and adults aged ≥13 in the past 2 weeks. Performing factor analysis to examine the factor structure of the BDI-II has both research and practical implications. From a practical perspective, treatment programs may not be equally effective for different depression subfactors. Hence, the identification of the factor structure of depression can improve comprehensive evaluations of intervention programs. From a theoretical standpoint, subgroup means are frequently examined and invariance of the factor structure is a prerequisite of group mean comparisons. Furthermore, the broad depression index lacks specificity. If subdimensions of depression are differentially associated with antecedents and consequences, then the use of a global depression dimension may account for the inconsistent findings in literature.
The Beck Depression Inventory–Second Edition
The BDI-II is a revised version of the BDI based on criteria from the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV; American Psychiatric Association, 1994). Four of 21 BDI items (Body Image Change, Work Difficulty, Weight Loss, and Somatic Preoccupation) were replaced with new items (Agitation, Worthlessness, Loss of Energy, and Concentration Difficulty) in the BDI-II. Nineteen of the 21 BDI-II items consist of four statements arranged on a continuum from less depressed to more depressed. Items of Changes in Sleeping Pattern and Changes in Appetite contain seven statements to differentiate an increase or decrease in sleep hours and appetite. That is, the seven options were 0, 1a, 1b, 2a, 2b, 3a, and 3b, with a higher rated option indicating an increase or decrease in either symptom. These modifications were mainly to address the DSM-IV criterion.
Although no items have been assigned formally to the BDI-II subscales, numerous studies were conducted to examine the dimensionality of the BDI-II. However, the results obtained by these studies were inconsistent. A meta-analysis that quantitatively synthesizes the factor structures of the BDI-II was therefore needed.
Previous Meta-Analyses
A meta-analysis by Shafer (2006) identified 33 studies reporting BDI pattern matrices. Studies from 1966 to 1999 yielded 13,643 participants. A three-factor solution seems best in terms of having an interpretable factor structure. The first factor, Negative Attitudes toward Self, was defined by 11 items. One of these 11 items, Body Image Change, was replaced in the BDI-II. The second factor, Performance Impairment, was defined by seven items. Two of these seven items, Work Difficulty and Somatic Preoccupation, were replaced in the BDI-II. The third factor, Somatic Concerns, was defined by three items. One (Weight Loss) of these three items was replaced in the BDI-II. The BDI-II is a refined version of the BDI, but with sufficient modifications that may potentially affect the factor structure. Whether the three-factor solution applies to the BDI-II is thus of interest. Furthermore, the factor structure of the BDI-II may vary as a function of various moderators. However, moderator analysis of the factor structure of depressive symptoms was not conducted by Shafer (2006).
Effect Sizes in Meta-Analysis of Exploratory Factor Analysis
Pattern matrix, correlation matrix, and covariance matrix are three effect sizes that can be used in a meta-analysis of factor analysis. The pattern matrix is an item-by-factor matrix that contains factor loadings indicating which items are involved in which factors and to what extent. Factor loadings are interpreted in a manner similar to how regression coefficients are interpreted in multiple regression analysis. Shafer (2005, 2006) used pattern matrices to construct co-occurrence matrices that were then subjected to exploratory factor analysis.
Covariance matrices are effect size statistics that can be applied in meta-analysis of factor analysis. Beretvas and Furlow (2006) developed a method for analyzing covariance matrices. After identifying studies that reported covariance matrices, raw covariance matrices were weighted and aggregated to construct a mean covariance matrix. The mean covariance matrix was then subjected to confirmatory factor analysis. As the covariance matrix among items is rarely reported in empirical studies, a meta-analysis of the covariance matrix is rare.
To avoid the limitations of previous meta-analyses, both pattern and covariance matrices were used as effect sizes. Exploratory factor analysis was applied to analyze mean standardized co-occurrence matrices derived from pattern matrices, while confirmatory factor analysis was applied to mean covariance matrices.
Moderators
Language Version
The meta-analysis by Kim, DeCoster, Huang, and Bryant (2013), which examined the effect of language on the factor structure of the Geriatric Depression Scale, analyzed 26 studies (N =14,669). Support for the effect of language was strong. A four-factor structure was supported for the full sample, while models with four to six factors were supported for the 10 languages. Penley (2001) compared the factor structures of the English and Spanish versions of the BDI-II using a sample of bilingual college students. The effect of language was small. As cross-cultural research (Al-Musawi, 2001; Chang, 2005) is especially interested in determining whether the factor structure obtained for Western cultures can be applied to non-Western cultures, one must explore the effect of language on the factor structure of the BDI-II.
Risk Level
The factor structure of the BDI-II must be invariant across groups such that the means of groups with different levels of depression risk can be compared. Beck, Steer, and Brown (1996) reported different factor structures for a student sample and a clinical sample. The Cognitive and Somatic-Affective factors were for the clinical participants, while the Cognitive-Affective and Somatic factors were for the student sample. The factor structure differed for normal and clinical samples for the Turkish version of the BDI-II in the study by Kapci, Uslu, Turkcapar, and Karoglan (2008), who sampled 203 normal adults and 176 depressive disorder outpatients. A Performance Difficulty-Somatic and Negative Attitude factors were found for the normal sample, while Somatic-Affective and Cognitive factors were for the outpatient sample. As primary research used the BDI-II to assess depression for general populations such as students (Al-Musawi, 2001; Chang, 2005; Dozois, Dobson, & Ahnberg, 1998), high-risk participants such as patients with chronic fatigue syndrome (Brown, Kaplan, & Jason, 2011), and clinical participants with a mental disorder/illness (Cole, Grossman, Prilliman, & Hunsaker, 2003), the factor structures of the BDI-II in these studies were inconsistent and warranted comparisons of the factor structures of the BDI-II across groups with differential risk factors for depression.
Age
Studies comparing the factor structure of the BDI-II across age groups were scarce, and the study by Segal, Coolidge, Cahill, and O’Riley (2008) was an exception. They compared the factor structure for 229 young adults (mean age = 19.60 years) recruited from psychology courses and 147 adults living in a community (mean age = 70.30 years). Although the one-factor solution was acceptable for both age groups, the salience of items varied. Nonetheless, the number of factors underlying the BDI-II varied in studies by Steer and colleagues (Steer, Ball, Ranieri, & Beck, 1999; Steer, Kumar, Ranieri, & Beck, 1998). More specifically, Steer et al. (1999) sampled 210 depressed adults (mean age = 41.29 years) and found that the two-factor solution was supported. On the other hand, Steer et al. (1998) sampled psychiatric patients (mean age = 15.17 years) and found that the three-factor solution was supported. Because empirical research has rarely examined the age effect on the factor structure of the BDI-II, this meta-analysis examined the possible effect of age.
Confirmatory Factor Analysis of the BDI-II
Several factor structure models, including the two-factor, three-factor, bifactor (specific and general depression factors), and first-order with second-order depression factors models, were tested in primary research. However, findings regarding the support of these models were inconsistent. For example, Titov et al. (2011) surveyed 172 depressed patients and found that the two-factor solution with the Cognitive and Somatic factors had a good fit to data. Corbière et al. (2011), who surveyed 206 patients with chronic pain, found that the three-factor solution with Cognitive, Affective, and Somatic factors had the best fit to data. Vanheule, Desmet, Groenvynck, Rosseel, and Fontaine (2008) tested the two models in Beck et al. (1996) as well as 10 alternative models using a clinical sample of 404 patients and a general sample of 695 adults. They found that the fit of the two-factor solution with Cognitive and Somatic-Affective factors in the clinical sample by Beck et al. (1996) and the three-factor solution with Cognitive, Affective, and Somatic factors by Buckley, Parker, and Heggie (2001) were acceptable.
Ward (2006) reanalyzed data from five studies consisting of six samples and found that the three-factor solution with a general factor and two specific depression factors best represented data. The solution with a general factor with two specific factors was also supported by Quilty, Zhang, and Bagby (2010), who surveyed 425 adult patients with major depression and found that the general factor with Somatic- and Cognitive factors fit data well. The solution with a general factor and three specific factors, the Cognitive, Affective, and Somatic factors, was supported by Arnarson, Ólason, Smári, and Sigurđsson (2008), who tested the factor structure of the Icelandic BDI-II using 1,206 students and 248 patients. Cross-country support for the presence of general depression with specific depression factors was also demonstrated by Brouwer, Meijer, and Zevalkink (2013), who surveyed a large sample of 1,530 patients to test the Dutch BDI-II, and Al-Turkait and Ohaeri (2010), who used 624 college students to test the factor structure of the Arabic BDI-II. Along a similar line, Harris and D’Eon (2008), who analyzed 481 Canadian patients with chronic pain, found that the fit to data of the model with three first-order factors, Negative Attitude, Performance Difficulty, and Somatic Elements, and a second-order factor was good. Given findings range widely, a meta-analysis is needed because it can identify the overall factor structure of the BDI-II. This study combined covariance matrices obtained by previous studies to extend and clarify previous findings.
Study 1
Method
Literature Search
To locate potential studies, the ERIC, PsycINFO, PubMed, and ProQuest Dissertations and Theses databases were searched up to March 2013. The search terms were the Beck Depression Inventory Second Edition, Beck Depression Inventory–II, and BDI-II combined with factor analysis, factor analyses, principal component analysis, principal component analyses, factor structure, factorial, validity, validation, item analysis, dimension, dimensionality, or psychometric. Included studies must meet the following criteria. First, studies must report correlation matrices or pattern matrices from exploratory factor analysis of the BDI-II. For studies reporting the pattern matrix, they must provide at least the highest factor loadings for BDII-II items. Furthermore, studies must be published in English. The studies included are listed in the references prefixed with an asterisk.
Analysis
For the use of pattern matrix as an effect size, the sample-size-weighted mean co-occurrence matrix, which served as the correlation matrix, was subjected to exploratory factor analysis. To compute a sample-size-weighted mean co-occurrence matrix, a raw co-occurrence matrix for each pair of the 21 BDI-II items was computed. When a pair of BDI-II items had their highest loading on the same factor and their factor loading was ≥.4, they were given a value of 1; otherwise, a value of 0 was assigned.
Some researchers did not administer all 21 BDI-II items to study participants. Specifically, Byrne, Stewart, and Lee, (2004), Lindsay and Skene (2007), and Palmer and Binks (2008) did not administer the item of Loss of Interest in Sex. Hence, sample size for Loss of Interest in Sex was smaller than those for the remaining 20 items. To compare co-occurrence matrices across studies, standardized co-occurrence was acquired by calculating the proportion of each pair of BDI-II items with the highest loadings on the same factor. That is, the standardized co-occurrence matrix was derived by dividing the number of times a pair of BDI-II items had their highest loadings on the same factor by the total number of times that a pair of BDI-II items was measured. The mean standardized co-occurrence matrix was then computed by averaging the sample-size-weighted standardized co-occurrence matrices. Conway and Huffcutt (2003) suggested that principal axis was generally a good factor extraction model and the oblique rotation was a preferred choice. As Promax rotation was the most commonly used rotation method in the included studies, factor analysis was performed via principal axis analysis followed by Promax rotation in the present study.
Results
Included Studies
This meta-analysis included 51 studies consisting of 62 independent samples involving 20,475 participants. Notably, some studies had overlapping samples. About half of the data Bedi (2001) analyzed was also analyzed in the studies by Beck et al. (1996) and Steer et al. (1999). In the study by Bos et al. (2009), 331 pregnant women were surveyed in their last trimester of pregnancy. Of all 331 women, 130 women and another new 184 mothers were tested at 3 months postpartum. As splitting overlapping participants among studies was not possible, these studies were considered independent.
Of the 51 studies, 42 were journal articles, 6 were doctoral dissertations, 2 were master’s theses, and 1 was a test manual. Table 1 lists sample size, mean age, gender, population type, language version, reliability coefficient in terms of α, factor extraction method, rotation method, number of factors retained, and percentage of variance explained. Average sample size was 330.24 participants (range = 51-2,095), and mean age was 32.86 years (range = 15-76). Seven samples were male only, 12 were female only, and 43 were mixed. Seventeen samples comprised college students. Of the 62 samples, the BDI-II version used and sample numbers were as follows: English BDI-II, 42 samples; Chinese BDI-II, 4 samples; Turkish BDI-II, 4 samples; Portuguese BDI-II, 3 samples; Spanish BDI-II, 3 samples; Arabic BDI-II, 2 samples; Japanese BDI-II, 1 sample; Croatian BDI-II, 1 sample; Malay BDI-II, 1 sample; and Xhosa BDI-II, 1 sample. The 21-item BDI-II was administered to 59 samples.
Included Studies.
Note. NA = not available/applicable. Extraction method, PA = principal axis; PC = principal component; EPI = equal prior instant communalities extraction; ML = maximum likelihood.
Six samples (Buckley et al., 2001; Carmody, 2005; Grothe et al., 2005; Johnson et al., 2006; Osman et al., 2008; Whisman et al., 2000) did not conduct exploratory factor analyses but provided correlation matrices. Three samples did not report the extraction method. Of the remaining 53 samples, 24 used principal axis analysis, 22 used principal components analysis, 6 used maximum likelihood, and 1 used equal prior instant communalities.
Of 56 samples providing information about exploratory analyses, 2 samples retained one factor, 37 samples retained two factors, 13 samples retained three factors, 2 samples retained four factors, 1 sample retained five factors, and 1 sample retained six factors. For the 54 samples that retained more than one factor, 30 used Promax rotation, 10 used Oblimin rotation, 9 used Varimax rotation, 1 used Quartimax rotation, 3 used some oblique rotation, and 1 sample did not report its rotation method. Of the 56 samples providing information about exploratory factor analyses, 20 did not report the percentage of variance accounted for by the retained factors. In the remaining 36 studies, mean variance explained was 47.96% (range = 30.24% to 89%).
As mentioned, pattern matrices were not reported in six samples. After principal axis analyses, Promax rotation was performed to examine the factor structure for these six samples. Based on the criterion proposed by Conway and Huffcutt (2003) and Henson and Roberts (2006), the two-factor solution was supported for studies by Grothe et al. (2005), Johnson et al. (2006), and Osman et al. (2008). The three-factor solution best represented data in the studies by Buckley et al. (2001), Carmody (2005), and Whisman et al. (2000).
Factor Analysis Results for the Full Sample
The upper diagonal of Table 2 is the raw co-occurrence matrix for BDI-II items. The best agreement between studies was for the relation between Items 20 and 15. Items of Tiredness or Fatigue and Loss of Energy were related in 56 of 62 samples. Exploratory factor analysis was performed using the sample-size-weighted mean co-occurrence matrix in the lower diagonal of Table 2.
Raw Co-Occurrence Matrix and Sample-Size-Weighted Standardized Co-Occurrence Matrix.
Note. The raw co-occurrence matrix is displayed in the upper diagonal and the sample size-weighted co-occurrence matrix is presented in the lower diagonal.
As most studies retained two or three factors, the two-factor and three-factor solutions were explored. Item 10 (Crying) did not have a salient (≥.4) loading in the two-factor solution, while Items 10 (Crying), 11 (Agitation), 13 (Indecisiveness), 17 (Irritability), and 21 (Loss of Interest in Sex) had no salient loadings in the three-factor solution. As the two-factor solution better approximated a simple structure, the two-factor solution was more acceptable than the three-factor solution. Table 3 presents the Promax-rotated pattern matrix for the two-factor solution.
Promax-Rotated Factor Structure for the BDI-II.
Note. Factor loadings equal to or greater than .40 are in boldface.
In the two-factor solution, the first two eigenvalues were 6.23 and 5.58. The correlation coefficient between these two factors was .17, much lower than that reported in the study by Beck et al. (1996). Factor 1 was related to nine depressive symptoms: Sadness, Pessimism, Past Failure, Guilty Feelings, Punishment Feelings, Self-Dislike, Self-Criticalness, Suicidal Thoughts or Wishes, and Worthlessness. This factor was called the Cognitive factor by Beck et al. (1996). Factor 2 consisted of 11 depressive symptoms. This factor was similar to the Somatic-Affective factor in the study by Beck et al. (1996) except that the Somatic-Affective factor in Beck et al. (1996) was also defined by the symptom of Crying. In summary, the factor structure for the full sample was similar to that for psychiatric outpatients in the study by Beck et al. (1996).
Comparison of Factor Analysis Between English and Non-English BDI-II Versions
As the two-factor solution better approximated a simple structure for the full sample, the two-factor solution was explored for each subgroup. Forty-two samples were administered the English BDI-II, involving 11,536 participants. The first two eigenvalues were 7.46 and 6.37. The correlation between these two factors was .15. Factor 1 consisted of 10 items, and was labeled Negative Attitudes by Harris and D’Eon (2008). Factor 2 was similar to the Somatic-Affective factor in the study by Beck et al. (1996).
Twenty samples used non-English versions of the BDI-II, consisting of 8,939 participants. The corresponding eigenvalues for non-English versions were 4.75 and 4.67. The correlation coefficient between the two factors was .19. Factor 1 resembled the Cognitive factor identified for the full sample. Factor 2 was similar to the Somatic-Affective factor identified for the full sample except Factor 2 was not defined by Loss of Interest in Sex. In sum, the factor structure for the non-English version was quite similar to that for the full sample.
Comparison of Factor Analysis Between the General and At-Risk/Clinical Samples
Twenty-five samples involving 10, 841 participants were selected from the general population. The first two eigenvalues were 5.38 and 4.80. The correlation coefficient between these two factors was .16. Factor 1 resembled the Cognitive factor identified in the full sample. Factor 2 was similar to the Somatic-Affective factor identified in the full sample except Factor 2 was not defined by Indecisiveness and Loss of Interest in Sex.
Thirty-seven samples consisting of 9,634 participants were selected from at-risk/clinical populations. The first two eigenvalues were 7.22 and 6.62. The correlation of these two factors was .15. The factor structure for at-risk/clinical samples was similar to that of the English BDI-II except the item of Agitation did not have a salient loading.
Comparison of Factor Analysis Between Youths/College Students and Adults
The main life tasks for youths and college students are preparation for career and marriage, while those for adults were engagement in career and marriage. As the life demands between youths/college students and adults were different, the age groups were categorized into youths/college students versus adults. Twenty-seven samples were selected from youths/college students (N = 10,347). The first two eigenvalues were 5.46 and 4.60. The correlation between these two factors was .14. Factor 1 was similar to the Cognitive factor identified in the full sample except that the Cognitive factor in the full sample was not defined by Indecisiveness. Factor 2 resembled the Somatic-Affective factor identified in the general samples.
Thirty-five samples consisting of 10,128 participants were selected from adults. The first two eigenvalues were 7.09 and 6.85. The correlation between these two factors was .16. The factor structure of the BDI-II for adults was similar to that of the English BDI-II.
Study 2
Method
Literature Search
Using search procedures described in Study 1, 13 studies were identified that reported covariance matrices among the BDI-II items. Beck et al. (1996) had two samples and Penley (2001) had three samples. In total, 16 independent samples involving 5,128 participants were used to examine the factor structure via covariance structure analysis.
Models
The following models were tested using LISREL 8 (Jöreskog & Sörbom, 1993)
Model 1, the two-correlated-factor model, identified in the full sample with a Cognitive factor (defined by Items 1-3, 5-9, and 14) and a Somatic-Affective factor (defined by Items 4, 11-13, and 15-21).
Model 2, the two-correlated-factor model, identified in the clinical samples in the study by Beck et al. (1996), had 12 items loading on a Somatic-Affective factor (Items 4, 10-13, and 15-21), and 9 items loading on a Cognitive factor.
Model 3, the two-correlated-factor model, identified in Dozois et al. (1998), had a Cognitive-Affective factor consisting of 10 items (Items 1-3, 5-9, 13, and 14) and a Somatic-Vegetative factor defined by 11 items (Items 4, 10-12, and 15-21).
Model 4 was the two-correlated-factor model identified by Steer et al. (1999) with a Cognitive factor defined by Items 2, 3, 5 to 9, and 14 and a non-Cognitive factor defined by the remaining items.
Model 5 was the three-correlated-factor model tested in Beck, Steer, Brown, and van der Does (2002), with a Cognitive factor consisting of seven items (Items 3, 5-8, 13, and 14), a Somatic factor consisting of nine items (Items 10, 11, and 15-21), and an Affective factor defined by five items (Items 1, 2, 4, 9, and 12).
Model 6 was the three-correlated-factor model used in the study by Buckley et al. (2001), with a Cognitive factor defined by nine items (Items 1-3, 5-9, and 14), an Affective factor defined by four items (Items 4, 10, 12, and 13), and a Somatic factor consisting of eight items (11 and 15-21).
Model 7 was the three-correlated-factor model tested by Osman et al. (1997), which had 10 items loading on Negative Attitudes (Items 1-3, 5-10, and 14), seven items loading on a Performance Difficulty factor (Items 4, 12, 13, 15, 17, 19, and 20), and four items loading Somatic Elements (Items 11, 16, 18, and 21).
As the general depression factor was proposed in previous research (Brouwer et al., 2013; Ward, 2006), an alternative set of models with a general depression factor was added to these seven models. For example, the alternative model for Model 1 was a model with a general factor defined by all items, Cognitive and Somatic-Affective factors.
To assess model adequacy, χ2 was derived to measure the difference between an a priori model and data. A significant χ2 value indicates that the tested model deviates from data and that a hypothesized model should be rejected. One limitation associated with the χ2 value is dependency on sample size. Hence, the Tucker–Lewis index, comparative fit index (CFI), and root mean square error of approximation (RMSEA) were applied. A value of .90 or greater for TLI indicates an acceptable fit from a practical stand point (Bentler, 1990). This is also the case for the CFI (Bentler, 1990). Conversely, an RMSEA value of .06 or less indicates good model fit (Hu & Bentler, 1999).
Results
Confirmatory factor analyses were performed using the sample-size-weighted mean covariance matrix (Table 4). Table 5 presents fit indices of all models. Although χ2 values for all models were statistically significant, comparative fit indices indicate that models fit well. Analytical results also show that the fit of the two-factor models (Models 1-4) was comparable to that of the three-factor models (Models 5-7). As the two-factor model was more parsimonious, it was considered superior. Although the fit of the alternative set of models (Models 1a-7a) to data was good, these models lacked empirical identification (Brunner, Nagy, & Wilhelm, 2012). Specifically, the covariance between the general and one of the depression subfactors was not identified in all seven alternative models; thus, alternative models were not considered.
Sample-Size-Weighted Mean Covariance Matrix.
Fit Indices.
Note. RMSEA = root mean square error of approximation; TLI = Tucker–Lewis index; CFI = comparative fit index. Models 1a to 7a were alternative models with a general depression factor and depression subfactors.
p < .01.
The correlation between latent constructs was strong in Models 1 to 4, demonstrating the existence of a considerable amount of shared variance (Table 6). To address the issue of highly correlated latent constructs, the one-factor model with a general depression factor was tested. The χ2 value was 4,256.17, df = 189. Although this χ2 value was statistically significant, the RMSEA, TLI, and CFI values were good at .07, .96, and .97, respectively, providing support for the one general depression factor from a practical standpoint.
Factor Loadings, Reliability Estimates, and Correlation Between Latent Constructs.
Note. C = a Cognitive factor; SA = a Somatic-Affective factor; SA = a Somatic-Affective factor; CA = a Cognitive-Affective factor; SV = a Somatic-Vegetative factor; NC = a non-Cognitive factor; A = an Affective factor; S = a Somatic factor; ND = a Negative Attitude factor; PD = a Performance Difficulty factor; SE = a Somatic Element factor; 1-f = the one-factor model; G = a General Depression factor.
All factor loadings (Table 6) were statistically significant, indicating that each latent construct was well defined and each item was influenced by its corresponding latent construct. Item 21, Loss of Interest in Sex, had the lowest factor loading. The latent construct accounts for roughly 12% to15% of variance in this item. How well the scale score represented the latent construct, indicated by ω, ranged from .24 to .79. That is, the proportion of variance accounted for by a latent construct was 24% to 79%. Thus, reliability of the depression subfactors varied markedly.
Discussion
The BDI-II is one of most popular inventories of depression. Given the widespread use of the BDI-II, examining its factor structure is important. This study examined the dimensionality of the BDI-II. Meta-analyses were used to combine findings of pattern and covariance matrices. On the basis of studies that conducted exploratory factor analysis, the BDI-II consists of Cognitive and Somatic-Affective factors. The two-factor structure identified in this study was similar to that obtained in the clinical study by Beck et al. (1996). This finding is inconsistent with the three-factor structure found by Shafer (2006). The factors of Performance Impairment and Somatic Concerns in Shafer (2006) combined to form the Somatic-Affective factor. The factor of Negative Attitudes was similar to the Cognitive factor.
Based on confirmatory factor analysis results of combined covariance matrices, the two-correlated-factor model was the best representation of data. All four two-correlated-factor models had a Cognitive or Cognitive-Affective factor defined by the core item Self-Dislike. The other factor in the four two-factor models was a Somatic-Affective, Somatic-Vegetative, or non-Cognitive factor defined by the core item Tiredness or Fatigue. The Somatic factor was also supported in the study by Shafer (2006).
Given the importance of the general depression factor proposed in the literature and the high correlation between latent constructs, models with a general depression factor and depression subfactors were explored. These models did not achieve empirical identification, likely due to factor overextraction (Chen, West, & Sousa, 2006; Rindskopf, 1984). Hence, the bifactor models with general and specific depression factors were not considered. To test the possible existence of a common depression factor, the one-factor model assuming all correlations between depression subfactors are equal to 1 was tested. The good fit of the one-factor model supported the existence of a general depression factor (Brouwer et al., 2013). The finding of a general depression factor does not necessarily invalidate the differentiation of specific depression factors as a different depression subfactor was reportedly related to different etiologies and external criteria (Abramson, Metalsky, & Alloy, 1989; Alloy, Just, & Panzarella, 1997; Payne, Palmer, & Joffe, 2009).
Based on exploratory factor analyses, refinement of the items Crying, Agitation, Indecisiveness, and Loss of Interest in Sex should be considered as these items did not have salient loadings in the full sample or some study subgroups. As these items were not a good depression marker, they should be revised in future BDI-II versions. On the basis of confirmatory factor analysis, refinement of the item Loss of Interest in Sex was further supported due to it having the lowest reliability among the 21 items.
The effect of language version on the factor structure was noted by Kim et al. (2013); therefore, the factor structures between English and non-English versions of the BDI-II were compared. Although the two-factor solutions were supported for these versions, factor patterns differed. Hence, comparison of mean depression across language versions revealed the true group differences among measured constructs and constructs with irrelevant variance. Culturally specific item adaptations of BDI-II items are recommended in future versions. For example, Bravo, Canino, Rubio-Stipec, and Woodbury-Fariña (1991) suggest a comprehensive model of translation and cultural adaption to assure sematic, content, technical, criterion, and conceptual equivalence. As such, the item wordings can be relevant to different cultures. The moderating effects of population type and age group were also supported. Nevertheless, invariance of a factor structure across subgroups of studies using confirmatory factor analysis was not tested in this study due to the small number of data points.
Although the weighted mean co-occurrence matrices were computed respectively for males and females, these matrices were not positive definite. The gender effect was thus not examined. Future research should address this issue. The effect of ethnicity on the factor structure of depression was explored in a previous meta-analysis (Kim, DeCoster, Huang, & Chiriboga, 2011). Examining the ethnicity effect with the few data available to this meta-analysis is not feasible. Future research should address this issue as mean depression scores were frequently compared across ethnicities in primary research (Cooper, 2010; Penley, 2001).
Footnotes
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was funded by National Science Council of the Republic of China, Taiwan under Grant No. NSC 101-2410-H-018-017.
