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Are alexithymia and depression distinct or overlapping constructs?: A study in a general population
Are Alexithymia and Depression Distinct or Overlapping Constructs?: A Study in a General Population Jukka Hintikka, Kirsi Honkalampi, Johannes Lehtonen, and Heimo Viinama¨ki The aim of this study was to investigate the relationship between alexithymia and depression in a general population sample (N ⴝ 1,888), as measured by the 20-item Toronto Alexithymia Scale (TAS-20) and the 21-item Beck Depression Inventory (BDI-21), using factor analysis. The items of the TAS-20 and the BDI-21 loaded on separate factors with only a minor overlap concerning physical worries. However, in a subset of
subjects, who were both alexithymic and depressed, loadings were highly overlapping. These findings suggest that alexithymia and depression may be highly associated. Another conclusion might be that psychometric properties of the TAS should be further developed to make differentiation between alexithymia and depression possible. Copyright © 2001 by W.B. Saunders Company
T
pressive to determine whether the two were distinct constructs in this subsample as well.
HE ALEXITHYMIA CONSTRUCT was formulated in early 1970s.1,2 Originally, alexithymia was defined as the inability to recognize and verbalize emotions.2 A recent view is that alexithymia reflects generally deficits in the cognitive processing of emotions, which remain undifferentiated and poorly regulated.3 Alexithymia has been found to be a risk factor for several somatic, psychosomatic, and psychiatric disorders.3-9 Some researchers have argued that alexithymia is a stable and unique personality trait,10,11 while others have suggested it is state-dependent and related to anxiety and depression.12,13 In their original factor analytic study, Parker et al.10 found that the items of Toronto Alexithymia Scale (TAS) and Beck Depression Inventory (BDI) loaded on separate factors, which suggests that alexithymia measured by the TAS and depression measured by the BDI are distinct psychological constructs. However, Parker et al. used the old 26-item version of the TAS and the short 13-item version of the BDI, and they had also selected samples.10 The aim of this study was to investigate whether the results of Parker’s factor analytic study10 could be replicated in a sample of general population, using the current 20-item version of TAS (TAS-20) and the 21-item BDI (BDI-21). We also performed separate analyses in a subset of subjects who were both alexithymic and moderately to severely de-
METHOD
Measurements The TAS-20 was developed in the early 1990s because of some shortcomings in the previous 26-item TAS.14,15 Bagby et al. found in their original validation study14 that the TAS-20 has a three-factor structure congruent with the alexithymia construct: difficulties identifying feelings (DIF), difficulties describing feelings (DDF), and externally oriented thinking (EOT). Other studies have supported the results of Bagby’s original work.16-18 The original English version of the TAS-20 had been previously translated into Finnish using a translation and blind backtranslation method. Moreover, a native speaker of English with an academic degree and a group of Finnish investigators had verified the accuracy, syntax, and cultural interpretation of each item. Finally, a confirmatory factor analysis had shown that the three-factor structure of the original scale was in agreement with the Finnish version.19 The Finnish version has also been previously used in studies on the general population.13,20 The TAS-20 score ranges from 20 to 100, and subjects scoring 61 or more have been suggested to be alexithymic while those scoring 51 or less are nonalexithymic.21 The BDI-21 was developed already in the early 1960s,22 and is probably still the most widely used self-rated depression scale. Factor analyses of the BDI-21 have yielded some inconsistent findings.23-26 Nevertheless, in all of these studies, the number of factors has been small, from one to three. It has been suggested that a score of 13 or less indicates minimal or mild depression, a score from 14 to 24 indicates moderate depression, and a score 25 or more indicates severe depression.27 The Finnish version of BDI-21 has been validated previously.28
Subjects From the Department of Psychiatry, Kuopio University Hospital, Kuopio, Finland. Address reprint requests to Jukka Hintikka, M.D., Department of Psychiatry, Kuopio University Hospital, PO Box 1777, FIN-70211 Kuopio, Finland. Copyright © 2001 by W.B. Saunders Company 0010-440X/01/4203-0012$35.00/0 doi:10.1053/comp.2001.23147 234
The total sample included 3,004 subjects between the ages of 25 and 64 years, living in the Province of Kuopio, Finland. They were randomly selected from the National Population Register. After fully describing the study to the subjects, written informed consent was obtained. Participation was completely voluntary. The study protocol was approved by the Research Ethics Committee of Kuopio University Hospital and Kuopio University.
Comprehensive Psychiatry, Vol. 42, No. 3 ( May/June), 2001: pp 234-239
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The study questionnaires were first mailed in April 1998, and again to the nonrespondents 4 to 5 weeks later. A total of 2,050 of study questionnaires were returned, resulting in a response rate of 68.2%. Among the respondents 1,888 subjects (62.9% of the total sample) completed both the TAS-20 and the BDI-21. This final sample included 1,042 females and 846 males (Table 1). Cronbach’s alpha for the TAS-20 was found to be 0.86 and for the BDI-21, 0.89.
Statistical Analyses The 20 items of TAS and the 21 items of BDI were intercorrelated. The matrix was assessed for psychometric adequacy using Bartlett’s test of sphericity, the Kaiser-Meyer-Olkin measure of sampling adequacy, and inspection of the off-diagonal elements of the anti-image covariants matrix. All of these measures suggested that the correlation matrix was suitable for factor analysis. According to Bartlett’s test of sphericity, the items were interdependent (2 ⫽ 12,716.3, df ⫽ 219, P ⬍ .001). The Kaiser-Meyer-Olkin measure of sampling adequacy was 0.95, indicating that the items belonged together psychometrically. Only 27 (1.6%) of the off-diagonal elements of the anti-image covariants matrix were greater than 0.09, which suggests that the matrix of covariances of the individual items approach a diagonal. Next we selected the number of factors. In previous studies it has been found that both the original TAS-2014 and the Finnish version of TAS-2019 have the same three-factor structure (Table 2). Because previous studies on the factor structure of the BDI-21 have provided inconsistent findings, we conducted a preliminary principal component analysis using the eigenvalue ⱖ1 criterion, and found a three-factor structure also in the BDI-21 (Table 2). We supposed that if alexithymia and depression were distinct constructs, the items of the BDI-21 and TAS-21 would load on separate factors. The conclusion was to rotate six factors to varimax solution in the final principal component analysis including all 41 items of the scales. A saturation ⱖ0.35 was retained to construct factors. Finally, we calculated Spearman correlation coefficients (rho) between total scores of the TAS-20 and the BDI-21, and also between the factor scores (I through VI). We conducted these calculations using both the whole unselected sample of a general population and a subset of subjects who were concomitantly alexithymic and moderately to severely depressive.
Table 1. Sociodemographic and Clinical Characteristics by Gender
Age (mean ⫾ SEM; yr) TAS-20 score (mean ⫾ SEM) BDI-21 score (mean ⫾ SEM) No. with ⬍ 9 years education (%) Duration of education (mean ⫾ SEM; yr) Married/cohabiting (%) Currently employed (%)
Males (n ⫽ 846)
Females (n ⫽ 1042)
44.7 ⫾ 0.4 46.3 ⫾ 0.4 5.5 ⫾ 0.2
43.7 ⫾ 0.3 42.0 ⫾ 0.4 6.0 ⫾ 0.2
4.9
2.3
12.1 ⫾ 0.1 46.7 69.5
12.7 ⫾ 0.1 53.3 66.3
RESULTS
Sample of the General Population The mean TAS-20 score was 43.9 (SD 11.7). A total of 1,412 subjects (74.8%) scored 51 or less, indicating an absence of alexithymic features, and 188 subjects (10.0%) scored ⱖ61, indicating the presence of alexithymia. The mean BDI-21 score was 5.8 (SD 6.6), and the distribution was as follows: 88.3% (n ⫽ 1,667) had minimal or mild depression and 11.7% (n ⫽ 221) had moderate to severe depression. The six-factor solution accounted for 48.6% of the total variance (Table 1). Factor I accounted for 12.2% of the total variance and comprised 12 BDI-21 items. The factor was labeled “negative self-attitude” (NSA). Factor II, which accounted for 11.7% of the total variance and comprised 11 TAS-21 items, was labeled “deficient emotional awareness” (DEA). Ten BDI-21 items and two TAS-20 items loaded on factor III, which accounted 10.2% for the total variance. Factor III was labeled “physical worry and performance impairment” (PWPI; Table 2). Factor IV accounted for 5.9% of the total variance and comprised five TAS-20 items. Factor IV was labeled “externally oriented thinking” (EOT). Factor V comprised five TAS-20 items and accounted for 5.4% of the total variance. It was labeled “externally oriented interaction” (EOI). Finally, factor VI comprised two BDI-21 items, accounted for 3.1% of the total variance, and was labeled “appetite and weight loss” (AWL; Table 2). A significant correlation was found between TAS-20 and BDI-21 total scores. All three TAS-20 factors (DEA, EOT, EOI) had a low correlation with BDI total score and one BDI-21 factor (PWPI) correlated slightly with TAS-20 total score, indicating some overlap between the BDI-21 and TAS-20 scales. Moreover, the NSA factor had low but significant correlations with the DEA and EOT factors. Finally, a very low but nearly significant correlation was found between the AWL and DEA factors (Table 3). Subjects Who Were Both Alexithymic and Depressive Ninety-seven subjects were both alexithymic and moderately to severely depressive. Among them, the six-factor solution accounted for 39.5% of the total variance.
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Table 2. Common Varimax-Rotated Six-Factor Solution for TAS-20 and BDI-21 Items Factor Item
TAS-20 items* Item 1 (DIF) Item 2 (DDF) Item 3 (DIF) Item 4 (DDF) Item 5 (EOT) Item 6 (DIF) Item 7 (DIF) Item 8 (EOT) Item 9 (DIF) Item 10 (EOT) Item 11 (DDF) Item 12 (DDF) Item 13 (DIF) Item 14 (DIF) Item 15 (EOT) Item 16 (EOT) Item 17 (DDF) Item 18 (EOT) Item 19 (EOT) Item 20 (EOT) BDI-21 items† Item 1 (NSA) Item 2 (NSA) Item 3 (NSA) Item 4 (NSA) Item 5 (NSA) Item 6 (NSA) Item 7 (NSA) Item 8 (NSA) Item 9 (NSA) Item 10 (NSA) Item 11 (PWPI) Item 12 (PWPI) Item 13 (PWPI) Item 14 (PWPI) Item 15 (PWPI) Item 16 (PWPI) Item 17 (PWPI) Item 18 (AWL) Item 19 (AWL) Item 20 (PWPI) Item 21 (PWPI)
I
II
III
0.307 0.186 0.162 ⫺0.008 ⫺0.126 0.183 0.123 ⫺0.051 0.160 ⫺0.046 0.107 0.153 0.273 0.191 0.041 0.017 0.162 0.149 0.153 ⫺0.071
0.626 0.655 0.436 0.311 0.017 0.641 0.632 0.188 0.740 0.041 0.641 0.524 0.649 0.604 0.209 0.016 0.463 0.111 0.038 0.157
0.271 0.166 0.482 0.062 0.072 0.172 0.383 0.045 0.266 0.041 0.128 0.074 0.262 0.246 0.072 ⫺0.033 0.054 0.050 0.061 0.135
0.657 0.616 0.670 0.550 0.649 0.580 0.712 0.536 0.563 0.535 0.334 0.369 0.430 0.349 0.199 0.238 0.170 0.303 0.053 0.127 0.197
0.093 0.075 0.227 0.175 0.221 0.111 0.176 0.243 0.151 0.093 0.171 0.134 0.199 0.127 0.099 0.174 0.163 0.085 0.014 0.260 0.152
0.317 0.321 0.165 0.430 0.213 0.027 0.168 0.234 0.054 0.237 0.428 0.465 0.467 0.443 0.664 0.567 0.703 0.277 ⫺0.002 0.569 0.588
IV
V
VI
0.136 0.257 0.006 0.637 0.626 0.002 0.017 0.023 0.037 0.709 0.151 0.012 0.115 0.014 0.117 0.048 0.261 0.620 0.630 0.169
0.079 0.163 0.015 ⫺0.090 0.018 0.143 0.008 0.478 0.017 0.248 0.212 0.218 0.148 0.045 0.693 0.752 0.413 0.030 0.277 0.626
0.028 ⫺0.024 0.195 0.070 0.095 0.038 0.135 0.007 0.050 0.031 ⫺0.041 ⫺0.025 0.040 0.019 ⫺0.055 0.047 ⫺0.183 ⫺0.008 ⫺0.002 0.117
0.050 0.072 0.051 0.102 0.033 ⫺0.053 0.039 0.054 0.015 ⫺0.020 0.018 0.166 0.120 0.068 0.060 0.048 0.038 0.028 0.032 0.017 0.088
0.012 0.021 0.079 0.080 ⫺0.063 ⫺0.030 ⫺0.070 0.042 ⫺0.032 ⫺0.027 0.045 0.175 0.114 ⫺0.020 0.064 0.055 0.038 0.034 0.036 ⫺0.039 0.055
0.060 0.031 0.027 ⫺0.027 ⫺0.037 0.162 ⫺0.062 ⫺0.121 0.129 0.193 0.024 ⫺0.127 ⫺0.082 ⫺0.112 0.163 0.094 0.025 0.546 0.800 0.099 ⫺0.043
NOTE. Factor loadings ⱖ 0.350 are shown in boldface. * Three-factor structure described by Bagby et al.14 † Three-factor structure found in this sample in preliminary principal component analysis using eigenvalue ⱖ 1 criterion. Abbreviations: DIF, difficulty identifying feelings; DDF, difficulty describing feelings; EOT, externally oriented thinking; NSA, negative self-attitude; PWPI, physical worry and performance impairment; AWL, appetite and weight loss.
Factor I accounted for 9.4% of the total variance and comprised 10 common BDI-21 items with the NSA factor in the general population sample. Factor II accounted for 6.7% of the total variance and comprised TAS-20 items 1, 2, and 3, and BDI-21 items 11, 15, 17, and 20. Four TAS-20
items (9, 10, 18, and 19) and three BDI-21 items (1, 2, and 12) loaded on factor III, which accounted for 6.2% of the total variance. Factor IV accounted for 5.9% of the total variance and comprised three TAS-20 items (6, 9, and 11) and three BDI-21 items (9, 18, and 21). Factor V comprised four
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Table 3. Spearman Correlation Coefficients Between BDI-21 and TAS-20 Total Scores and Six Common Factors Factor Item
I
II
III
IV
V
VI
TAS-20
Factor II Factor III Factor IV Factor V Factor VI TAS-20 BDI-21
⫺.079† ⫺.155† ⫺.073† .026 ⫺.190† .011 .365†
⫺.024 .067† .010 ⫺.052* .708† .296†
⫺.010 .040 ⫺.107† .157† .613†
.064† ⫺.009 .467† .131†
⫺.004 .468† .062†
⫺.036 ⫺.086†
.506†
NOTE. Factors II (DEA), IV (EOT), and V (EOI) are TAS-20 factors; Factors I (NSA), III (PWPI), and VI (AWL) are BDI-21 factors. *P ⬍ 0.05. †P ⬍ .01.
TAS-20 items (12, 15, 17, and 20) and accounted for 5.8% of the total variance. Finally, factor VI, which comprised three TAS-20 items (4, 5, and 8) and two BDI-21 items (14, 19), accounted for 3.1% of the total variance. No significant correlations were found between these factors. Factors II, IV, and V correlated with the TAS-20 total score (respectively, Spearman’s rho ⫽ .252 [P ⬍ .05], .388 [P ⬍ .01], and .540 [P ⬍ .01]). Factor I (rho ⫽ .692 [P ⬍ .01]), factor II (rho ⫽ .488 [P ⬍ .01]), factor III (.246 [P ⬍ .05]), and factor IV (rho ⫽ .268 [P ⬍ .01] correlated with the BDI-21 total score. DISCUSSION
The items of the TAS-20 and the BDI-21 loaded on separate factors with only a minor overlap concerning physical worries in a sample of general population where most subjects were nonalexithymic and nondepressive. This strongly suggested that alexithymia measured by the TAS-20 and depression measured by the BDI-21 were mainly distinct psychological constructs. This finding is in line with the original factor analysis study conducted by Parker et al., who also found that the TAS and the BDI have only minor overlap.10 Nevertheless, in a subset of subjects who were both alexithymic and depressive, the factor solution was found to be very different. Only the NSA factor of the BDI remained completely the same. The loadings of other items of the TAS-20 and the BDI-21 on the other five factors were highly overlapping. According to our findings, alexithymic features measured by the TAS-20 and depressive symptoms measured by the BDI-21 are both distinct and overlapping. In populations where most subjects have neither alexithymia nor depression, the
TAS-20 and the BDI-21 measure mainly distinct psychological constructs. In alexithymic and moderately depressed subjects the TAS-20 and the BDI-21 measure highly overlapping constructs. There are two possible conclusions. First, alexithymia may be highly associated with depression, as has been suggested by some previous studies.12,13 As a consequence, the measures assessing these constructs will inevitably overlap if the subjects who are evaluated are moderately to severely depressive. Second, if we suppose that alexithymia and depression are distinct constructs, the psychometric properties of the TAS would have to be further developed to make differentiation possible. The three-factor structure found in the TAS-20 in a sample of the Finnish general population is somewhat different from the original three-factor structure described by Bagby et al.14 The original factors DIF and DFF formed one DEA factor. The original EOT factor was divided into two factors. The first EOT included items that described directly the way of thinking, the other (EOI) included items that described interactions and other externally oriented behavior preferences. A similar factor structure of the TAS-20 was found in a study of psychoactive substance–abusing inpatients.29 The researchers suggested that the TAS-20 might be a multidimensional scale. Another view is that the core of alexithymia construct is stable in different populations, producing a modest reliability in factor structure of the TAS-20. Nevertheless, the borders of the alexithymia construct may be population- and culture-dependent.30 The three-factor structure found for the BDI-21 in the general population is quite similar to that reported by Bennett et al. in a study of depressive adolescents.26 Golin and Hartz found only one
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well-defined hopelessness factor for the BDI-21.23 Two recent studies have yielded two-factor solutions including general depression (cognitive) and somatic disturbances (vegetative) factors.24,25 The main difference between our findings and those of Louks et al.24 and Shek25 is that in our sample “appetite and weight loss” was an independent third factor. Similar to the TAS-20 and alexithymia, the core of depression as measured by the BDI-21 seems to be stable, producing a modest reliability in factor structure in different populations. Here again, however, the frontiers of factors may be population- and culture-dependent. Parker et al. used the old 26-item version of the TAS and the short 13-item version of the BDI in their original work.10 Their two samples were smaller and included only university students (n ⫽ 406) and psychiatric outpatients (n ⫽ 164). As far
as we know, this is the first factor analytic study on the relationship between alexithymia and depression in a large sample of the general population. This is one of the strengths of our study. One of the limitations is that we used only self-reports. The study design would have been strengthened if we had interviewed a subsample of subjects to confirm that those who scored high on the BDI-21 were depressed and those who scored high on the TAS-20 were alexithymic. Another limitation concerns the cutoff scores used with the TAS-20, which are still preliminary.21 Our conclusion is that there remains a need to study associations between alexithymia and depression. For example, only longitudinal studies would help us to determine whether subjects are prone to be more alexithymic when they are depressed.
REFERENCES 1. Nemiah JC, Sifneos PE. Affect and fantasy in patients with psychosomatic disorders. In: Hill OV (ed): Modern Trends in Psychosomatic Mediscine, vol. 2. London, UK: Butterworths, 1970:26-34. 2. Sifneos PE. The prevalence of ‘alexithymic’ characteristics in psychosomatic patients. Psychother Psychosom 1973;22: 255-262. 3. Taylor GJ, Bagby RM, Parker JD. The alexithymia construct. A potential paradigm for psychosomatic medicine. Psychosomatics 1991;32:153-164. 4. Zeitlin SB, McNally RJ. Alexithymia and anxiety sensitivity in panic disorder and obsessive-compulsive disorder. Am J Psychiatry 1993;150:658-660. 5. Kauhanen J, Kaplan GA, Cohen RD, Julkunen J, Salonen JT. Alexithymia and risk of death in middle-aged men. J Psychosom Res 1996;41:541-549. 6. Todarello O, Casamassima A, Daniele S, Marinaccio M, Fanciullo F, Valentino L et al. Alexithymia, immunity and cervical intraepithelial neoplasia: replication. Psychother Psychosom 1997;66:208-213. 7. Rastam M, Gillberg C, Gillberg IC, Johansson M. Alexithymia in anorexia nervosa: a controlled study using the 20item Toronto Alexithymia Scale. Acta Psychiatr Scand 1997; 95:385-388. 8. Kooiman CG. The status of alexithymia as a risk factor in medically unexplained physical symptoms. Compr Psychiatry 1998;39:152-159. 9. Numata Y, Ogata Y, Oike Y, Matsumura T, Shimada K. A psychobehavioral factor, alexithymia, is related to coronary spasm. Jpn Circ J 1998;62:409-413. 10. Parker JD, Bagby RM, Taylor GJ. Alexithymia and depression: distinct or overlapping constructs? Compr Psychiatry 1991;32:387-394. 11. Wise TN, Mann LS, Shay L. Alexithymia and the fivefactor model of personality. Compr Psychiatry 1992;33:147151. 12. Hendryx MS, Haviland MG, Shaw DG. Dimensions of
alexithymia and their relationships to anxiety and depression. J Pers Assess 1991;56:227-237. 13. Honkalampi K, Hintikka J, Tanskanen A, Lehtonen J, Viinamaki H. Depression is strongly associated with alexithymia in the general population. J Psychosom Res 2000;48:99104. 14. Bagby RM, Parker JD, Taylor GJ. The twenty-item Toronto Alexithymia Scale—I. Item selection and cross-validation of the factor structure. J Psychosom Res 1994;38:23-32. 15. Bagby RM, Taylor GJ, Parker JD. The Twenty-item Toronto Alexithymia Scale—II. Convergent, discriminant, and concurrent validity. J Psychosom Res 1994;38:33-40. 16. Bach M, Bach D, de Zwaan M, Serim M, Bohmer F. Validation of the German version of the 20-item Toronto Alexithymia Scale in normal persons and psychiatric patients. Psychother Psychosom Med Psychol 1996;46:23-28. 17. Bressi C, Taylor G, Parker J, Bressi S, Brambilla V, Aguglia E, et al. Cross validation of the factor structure of the 20-item Toronto Alexithymia Scale: an Italian multicenter study. J Psychosom Res 1996;41:551-559. 18. Pandey R, Mandal MK, Taylor GJ, Parker JD. Crosscultural alexithymia: development and validation of a Hindi translation of the 20-item Toronto Alexithymia Scale. J Clin Psychol 1996;52:173-176. 19. Joukamaa M, Miettunen J, Kokkonen P, Koskinen M, Julkunen J, Kauhanen J, et al. Psychometric properties of the Finnish 20-item Toronto Alexithymia Scale. Nord J Psychiatry (in press). 20. Salminen JK, Saarijarvi S, Aarela E, Toikka T, Kauhanen J. Prevalence of alexithymia and its association with sociodemographic variables in the general population of Finland. J Psychosom Res 1999;46:75-82. 21. Taylor GJ, Bagby RM, Parker JDA. Disorders of affect regulation. Cambridge, UK: Cambridge University Press, 1997. 22. Beck AT, Ward CH, Mendelson M, Mock J, Erhaugh J. An inventory for measuring depression. Arch Gen Psychiatry 1961;4:53-63.
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23. Golin S, Hartz MA. A factor analysis of the Beck Depression Inventory in a mildly depressed population. J Clin Psychol 1979;35:322-325. 24. Louks J, Hayne C, Smith J. Replicated factor structure of the Beck Depression Inventory. J Nerv Ment Dis 1989;177:473479. 25. Shek DT. Reliability and factorial structure of the Chinese version of the Beck Depression Inventory. J Clin Psychol 1990;46:35-43. 26. Bennett DS, Ambrosini PJ, Bianchi M, Barnett D, Metz C, Rabinovich H. Relationship of Beck Depression Inventory factors to depression among adolescents. J Affect Disord 1997; 45:127-134.
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27. Schwab J, Bialow M, Clemmons R, Martin P, Holzer C. The Beck Depression Inventory with medical inpatients. Acta Psychiatr Scand 1967;43:255-266. 28. Raitasalo R. Depression and its connections with the need for psychotherapy. Kansanela¨kelaitoksen julkaisuja A:13. Vammala, Finland: Vammalan Kirjapaino Oy, 1977. 29. Haviland MG, Reise SP. Structure of the twenty-item Toronto Alexithymia Scale. J Pers Assess 1996;66:116-125. 30. Fukunishi I, Nakagawa T, Nakamura H, Kikuchi M, Takubo M. Is alexithymia a culture-bound construct? Validity and reliability of the Japanese versions of the 20-item Toronto Alexithymia Scale and modified Beth Israel Hospital Psychosomatic Questionnaire. Psychol Rep 1997;80:787-799.
subjects, who were both alexithymic and depressed, loadings were highly overlapping. These findings suggest that alexithymia and depression may be highly associated. Another conclusion might be that psychometric properties of the TAS should be further developed to make differentiation between alexithymia and depression possible. Copyright © 2001 by W.B. Saunders Company
T
pressive to determine whether the two were distinct constructs in this subsample as well.
HE ALEXITHYMIA CONSTRUCT was formulated in early 1970s.1,2 Originally, alexithymia was defined as the inability to recognize and verbalize emotions.2 A recent view is that alexithymia reflects generally deficits in the cognitive processing of emotions, which remain undifferentiated and poorly regulated.3 Alexithymia has been found to be a risk factor for several somatic, psychosomatic, and psychiatric disorders.3-9 Some researchers have argued that alexithymia is a stable and unique personality trait,10,11 while others have suggested it is state-dependent and related to anxiety and depression.12,13 In their original factor analytic study, Parker et al.10 found that the items of Toronto Alexithymia Scale (TAS) and Beck Depression Inventory (BDI) loaded on separate factors, which suggests that alexithymia measured by the TAS and depression measured by the BDI are distinct psychological constructs. However, Parker et al. used the old 26-item version of the TAS and the short 13-item version of the BDI, and they had also selected samples.10 The aim of this study was to investigate whether the results of Parker’s factor analytic study10 could be replicated in a sample of general population, using the current 20-item version of TAS (TAS-20) and the 21-item BDI (BDI-21). We also performed separate analyses in a subset of subjects who were both alexithymic and moderately to severely de-
METHOD
Measurements The TAS-20 was developed in the early 1990s because of some shortcomings in the previous 26-item TAS.14,15 Bagby et al. found in their original validation study14 that the TAS-20 has a three-factor structure congruent with the alexithymia construct: difficulties identifying feelings (DIF), difficulties describing feelings (DDF), and externally oriented thinking (EOT). Other studies have supported the results of Bagby’s original work.16-18 The original English version of the TAS-20 had been previously translated into Finnish using a translation and blind backtranslation method. Moreover, a native speaker of English with an academic degree and a group of Finnish investigators had verified the accuracy, syntax, and cultural interpretation of each item. Finally, a confirmatory factor analysis had shown that the three-factor structure of the original scale was in agreement with the Finnish version.19 The Finnish version has also been previously used in studies on the general population.13,20 The TAS-20 score ranges from 20 to 100, and subjects scoring 61 or more have been suggested to be alexithymic while those scoring 51 or less are nonalexithymic.21 The BDI-21 was developed already in the early 1960s,22 and is probably still the most widely used self-rated depression scale. Factor analyses of the BDI-21 have yielded some inconsistent findings.23-26 Nevertheless, in all of these studies, the number of factors has been small, from one to three. It has been suggested that a score of 13 or less indicates minimal or mild depression, a score from 14 to 24 indicates moderate depression, and a score 25 or more indicates severe depression.27 The Finnish version of BDI-21 has been validated previously.28
Subjects From the Department of Psychiatry, Kuopio University Hospital, Kuopio, Finland. Address reprint requests to Jukka Hintikka, M.D., Department of Psychiatry, Kuopio University Hospital, PO Box 1777, FIN-70211 Kuopio, Finland. Copyright © 2001 by W.B. Saunders Company 0010-440X/01/4203-0012$35.00/0 doi:10.1053/comp.2001.23147 234
The total sample included 3,004 subjects between the ages of 25 and 64 years, living in the Province of Kuopio, Finland. They were randomly selected from the National Population Register. After fully describing the study to the subjects, written informed consent was obtained. Participation was completely voluntary. The study protocol was approved by the Research Ethics Committee of Kuopio University Hospital and Kuopio University.
Comprehensive Psychiatry, Vol. 42, No. 3 ( May/June), 2001: pp 234-239
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The study questionnaires were first mailed in April 1998, and again to the nonrespondents 4 to 5 weeks later. A total of 2,050 of study questionnaires were returned, resulting in a response rate of 68.2%. Among the respondents 1,888 subjects (62.9% of the total sample) completed both the TAS-20 and the BDI-21. This final sample included 1,042 females and 846 males (Table 1). Cronbach’s alpha for the TAS-20 was found to be 0.86 and for the BDI-21, 0.89.
Statistical Analyses The 20 items of TAS and the 21 items of BDI were intercorrelated. The matrix was assessed for psychometric adequacy using Bartlett’s test of sphericity, the Kaiser-Meyer-Olkin measure of sampling adequacy, and inspection of the off-diagonal elements of the anti-image covariants matrix. All of these measures suggested that the correlation matrix was suitable for factor analysis. According to Bartlett’s test of sphericity, the items were interdependent (2 ⫽ 12,716.3, df ⫽ 219, P ⬍ .001). The Kaiser-Meyer-Olkin measure of sampling adequacy was 0.95, indicating that the items belonged together psychometrically. Only 27 (1.6%) of the off-diagonal elements of the anti-image covariants matrix were greater than 0.09, which suggests that the matrix of covariances of the individual items approach a diagonal. Next we selected the number of factors. In previous studies it has been found that both the original TAS-2014 and the Finnish version of TAS-2019 have the same three-factor structure (Table 2). Because previous studies on the factor structure of the BDI-21 have provided inconsistent findings, we conducted a preliminary principal component analysis using the eigenvalue ⱖ1 criterion, and found a three-factor structure also in the BDI-21 (Table 2). We supposed that if alexithymia and depression were distinct constructs, the items of the BDI-21 and TAS-21 would load on separate factors. The conclusion was to rotate six factors to varimax solution in the final principal component analysis including all 41 items of the scales. A saturation ⱖ0.35 was retained to construct factors. Finally, we calculated Spearman correlation coefficients (rho) between total scores of the TAS-20 and the BDI-21, and also between the factor scores (I through VI). We conducted these calculations using both the whole unselected sample of a general population and a subset of subjects who were concomitantly alexithymic and moderately to severely depressive.
Table 1. Sociodemographic and Clinical Characteristics by Gender
Age (mean ⫾ SEM; yr) TAS-20 score (mean ⫾ SEM) BDI-21 score (mean ⫾ SEM) No. with ⬍ 9 years education (%) Duration of education (mean ⫾ SEM; yr) Married/cohabiting (%) Currently employed (%)
Males (n ⫽ 846)
Females (n ⫽ 1042)
44.7 ⫾ 0.4 46.3 ⫾ 0.4 5.5 ⫾ 0.2
43.7 ⫾ 0.3 42.0 ⫾ 0.4 6.0 ⫾ 0.2
4.9
2.3
12.1 ⫾ 0.1 46.7 69.5
12.7 ⫾ 0.1 53.3 66.3
RESULTS
Sample of the General Population The mean TAS-20 score was 43.9 (SD 11.7). A total of 1,412 subjects (74.8%) scored 51 or less, indicating an absence of alexithymic features, and 188 subjects (10.0%) scored ⱖ61, indicating the presence of alexithymia. The mean BDI-21 score was 5.8 (SD 6.6), and the distribution was as follows: 88.3% (n ⫽ 1,667) had minimal or mild depression and 11.7% (n ⫽ 221) had moderate to severe depression. The six-factor solution accounted for 48.6% of the total variance (Table 1). Factor I accounted for 12.2% of the total variance and comprised 12 BDI-21 items. The factor was labeled “negative self-attitude” (NSA). Factor II, which accounted for 11.7% of the total variance and comprised 11 TAS-21 items, was labeled “deficient emotional awareness” (DEA). Ten BDI-21 items and two TAS-20 items loaded on factor III, which accounted 10.2% for the total variance. Factor III was labeled “physical worry and performance impairment” (PWPI; Table 2). Factor IV accounted for 5.9% of the total variance and comprised five TAS-20 items. Factor IV was labeled “externally oriented thinking” (EOT). Factor V comprised five TAS-20 items and accounted for 5.4% of the total variance. It was labeled “externally oriented interaction” (EOI). Finally, factor VI comprised two BDI-21 items, accounted for 3.1% of the total variance, and was labeled “appetite and weight loss” (AWL; Table 2). A significant correlation was found between TAS-20 and BDI-21 total scores. All three TAS-20 factors (DEA, EOT, EOI) had a low correlation with BDI total score and one BDI-21 factor (PWPI) correlated slightly with TAS-20 total score, indicating some overlap between the BDI-21 and TAS-20 scales. Moreover, the NSA factor had low but significant correlations with the DEA and EOT factors. Finally, a very low but nearly significant correlation was found between the AWL and DEA factors (Table 3). Subjects Who Were Both Alexithymic and Depressive Ninety-seven subjects were both alexithymic and moderately to severely depressive. Among them, the six-factor solution accounted for 39.5% of the total variance.
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Table 2. Common Varimax-Rotated Six-Factor Solution for TAS-20 and BDI-21 Items Factor Item
TAS-20 items* Item 1 (DIF) Item 2 (DDF) Item 3 (DIF) Item 4 (DDF) Item 5 (EOT) Item 6 (DIF) Item 7 (DIF) Item 8 (EOT) Item 9 (DIF) Item 10 (EOT) Item 11 (DDF) Item 12 (DDF) Item 13 (DIF) Item 14 (DIF) Item 15 (EOT) Item 16 (EOT) Item 17 (DDF) Item 18 (EOT) Item 19 (EOT) Item 20 (EOT) BDI-21 items† Item 1 (NSA) Item 2 (NSA) Item 3 (NSA) Item 4 (NSA) Item 5 (NSA) Item 6 (NSA) Item 7 (NSA) Item 8 (NSA) Item 9 (NSA) Item 10 (NSA) Item 11 (PWPI) Item 12 (PWPI) Item 13 (PWPI) Item 14 (PWPI) Item 15 (PWPI) Item 16 (PWPI) Item 17 (PWPI) Item 18 (AWL) Item 19 (AWL) Item 20 (PWPI) Item 21 (PWPI)
I
II
III
0.307 0.186 0.162 ⫺0.008 ⫺0.126 0.183 0.123 ⫺0.051 0.160 ⫺0.046 0.107 0.153 0.273 0.191 0.041 0.017 0.162 0.149 0.153 ⫺0.071
0.626 0.655 0.436 0.311 0.017 0.641 0.632 0.188 0.740 0.041 0.641 0.524 0.649 0.604 0.209 0.016 0.463 0.111 0.038 0.157
0.271 0.166 0.482 0.062 0.072 0.172 0.383 0.045 0.266 0.041 0.128 0.074 0.262 0.246 0.072 ⫺0.033 0.054 0.050 0.061 0.135
0.657 0.616 0.670 0.550 0.649 0.580 0.712 0.536 0.563 0.535 0.334 0.369 0.430 0.349 0.199 0.238 0.170 0.303 0.053 0.127 0.197
0.093 0.075 0.227 0.175 0.221 0.111 0.176 0.243 0.151 0.093 0.171 0.134 0.199 0.127 0.099 0.174 0.163 0.085 0.014 0.260 0.152
0.317 0.321 0.165 0.430 0.213 0.027 0.168 0.234 0.054 0.237 0.428 0.465 0.467 0.443 0.664 0.567 0.703 0.277 ⫺0.002 0.569 0.588
IV
V
VI
0.136 0.257 0.006 0.637 0.626 0.002 0.017 0.023 0.037 0.709 0.151 0.012 0.115 0.014 0.117 0.048 0.261 0.620 0.630 0.169
0.079 0.163 0.015 ⫺0.090 0.018 0.143 0.008 0.478 0.017 0.248 0.212 0.218 0.148 0.045 0.693 0.752 0.413 0.030 0.277 0.626
0.028 ⫺0.024 0.195 0.070 0.095 0.038 0.135 0.007 0.050 0.031 ⫺0.041 ⫺0.025 0.040 0.019 ⫺0.055 0.047 ⫺0.183 ⫺0.008 ⫺0.002 0.117
0.050 0.072 0.051 0.102 0.033 ⫺0.053 0.039 0.054 0.015 ⫺0.020 0.018 0.166 0.120 0.068 0.060 0.048 0.038 0.028 0.032 0.017 0.088
0.012 0.021 0.079 0.080 ⫺0.063 ⫺0.030 ⫺0.070 0.042 ⫺0.032 ⫺0.027 0.045 0.175 0.114 ⫺0.020 0.064 0.055 0.038 0.034 0.036 ⫺0.039 0.055
0.060 0.031 0.027 ⫺0.027 ⫺0.037 0.162 ⫺0.062 ⫺0.121 0.129 0.193 0.024 ⫺0.127 ⫺0.082 ⫺0.112 0.163 0.094 0.025 0.546 0.800 0.099 ⫺0.043
NOTE. Factor loadings ⱖ 0.350 are shown in boldface. * Three-factor structure described by Bagby et al.14 † Three-factor structure found in this sample in preliminary principal component analysis using eigenvalue ⱖ 1 criterion. Abbreviations: DIF, difficulty identifying feelings; DDF, difficulty describing feelings; EOT, externally oriented thinking; NSA, negative self-attitude; PWPI, physical worry and performance impairment; AWL, appetite and weight loss.
Factor I accounted for 9.4% of the total variance and comprised 10 common BDI-21 items with the NSA factor in the general population sample. Factor II accounted for 6.7% of the total variance and comprised TAS-20 items 1, 2, and 3, and BDI-21 items 11, 15, 17, and 20. Four TAS-20
items (9, 10, 18, and 19) and three BDI-21 items (1, 2, and 12) loaded on factor III, which accounted for 6.2% of the total variance. Factor IV accounted for 5.9% of the total variance and comprised three TAS-20 items (6, 9, and 11) and three BDI-21 items (9, 18, and 21). Factor V comprised four
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Table 3. Spearman Correlation Coefficients Between BDI-21 and TAS-20 Total Scores and Six Common Factors Factor Item
I
II
III
IV
V
VI
TAS-20
Factor II Factor III Factor IV Factor V Factor VI TAS-20 BDI-21
⫺.079† ⫺.155† ⫺.073† .026 ⫺.190† .011 .365†
⫺.024 .067† .010 ⫺.052* .708† .296†
⫺.010 .040 ⫺.107† .157† .613†
.064† ⫺.009 .467† .131†
⫺.004 .468† .062†
⫺.036 ⫺.086†
.506†
NOTE. Factors II (DEA), IV (EOT), and V (EOI) are TAS-20 factors; Factors I (NSA), III (PWPI), and VI (AWL) are BDI-21 factors. *P ⬍ 0.05. †P ⬍ .01.
TAS-20 items (12, 15, 17, and 20) and accounted for 5.8% of the total variance. Finally, factor VI, which comprised three TAS-20 items (4, 5, and 8) and two BDI-21 items (14, 19), accounted for 3.1% of the total variance. No significant correlations were found between these factors. Factors II, IV, and V correlated with the TAS-20 total score (respectively, Spearman’s rho ⫽ .252 [P ⬍ .05], .388 [P ⬍ .01], and .540 [P ⬍ .01]). Factor I (rho ⫽ .692 [P ⬍ .01]), factor II (rho ⫽ .488 [P ⬍ .01]), factor III (.246 [P ⬍ .05]), and factor IV (rho ⫽ .268 [P ⬍ .01] correlated with the BDI-21 total score. DISCUSSION
The items of the TAS-20 and the BDI-21 loaded on separate factors with only a minor overlap concerning physical worries in a sample of general population where most subjects were nonalexithymic and nondepressive. This strongly suggested that alexithymia measured by the TAS-20 and depression measured by the BDI-21 were mainly distinct psychological constructs. This finding is in line with the original factor analysis study conducted by Parker et al., who also found that the TAS and the BDI have only minor overlap.10 Nevertheless, in a subset of subjects who were both alexithymic and depressive, the factor solution was found to be very different. Only the NSA factor of the BDI remained completely the same. The loadings of other items of the TAS-20 and the BDI-21 on the other five factors were highly overlapping. According to our findings, alexithymic features measured by the TAS-20 and depressive symptoms measured by the BDI-21 are both distinct and overlapping. In populations where most subjects have neither alexithymia nor depression, the
TAS-20 and the BDI-21 measure mainly distinct psychological constructs. In alexithymic and moderately depressed subjects the TAS-20 and the BDI-21 measure highly overlapping constructs. There are two possible conclusions. First, alexithymia may be highly associated with depression, as has been suggested by some previous studies.12,13 As a consequence, the measures assessing these constructs will inevitably overlap if the subjects who are evaluated are moderately to severely depressive. Second, if we suppose that alexithymia and depression are distinct constructs, the psychometric properties of the TAS would have to be further developed to make differentiation possible. The three-factor structure found in the TAS-20 in a sample of the Finnish general population is somewhat different from the original three-factor structure described by Bagby et al.14 The original factors DIF and DFF formed one DEA factor. The original EOT factor was divided into two factors. The first EOT included items that described directly the way of thinking, the other (EOI) included items that described interactions and other externally oriented behavior preferences. A similar factor structure of the TAS-20 was found in a study of psychoactive substance–abusing inpatients.29 The researchers suggested that the TAS-20 might be a multidimensional scale. Another view is that the core of alexithymia construct is stable in different populations, producing a modest reliability in factor structure of the TAS-20. Nevertheless, the borders of the alexithymia construct may be population- and culture-dependent.30 The three-factor structure found for the BDI-21 in the general population is quite similar to that reported by Bennett et al. in a study of depressive adolescents.26 Golin and Hartz found only one
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well-defined hopelessness factor for the BDI-21.23 Two recent studies have yielded two-factor solutions including general depression (cognitive) and somatic disturbances (vegetative) factors.24,25 The main difference between our findings and those of Louks et al.24 and Shek25 is that in our sample “appetite and weight loss” was an independent third factor. Similar to the TAS-20 and alexithymia, the core of depression as measured by the BDI-21 seems to be stable, producing a modest reliability in factor structure in different populations. Here again, however, the frontiers of factors may be population- and culture-dependent. Parker et al. used the old 26-item version of the TAS and the short 13-item version of the BDI in their original work.10 Their two samples were smaller and included only university students (n ⫽ 406) and psychiatric outpatients (n ⫽ 164). As far
as we know, this is the first factor analytic study on the relationship between alexithymia and depression in a large sample of the general population. This is one of the strengths of our study. One of the limitations is that we used only self-reports. The study design would have been strengthened if we had interviewed a subsample of subjects to confirm that those who scored high on the BDI-21 were depressed and those who scored high on the TAS-20 were alexithymic. Another limitation concerns the cutoff scores used with the TAS-20, which are still preliminary.21 Our conclusion is that there remains a need to study associations between alexithymia and depression. For example, only longitudinal studies would help us to determine whether subjects are prone to be more alexithymic when they are depressed.
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