Is there a reliable factorial structure in the 20-item Toronto Alexithymia Scale?: A comparison of factor models in clinical and normal adult samples
Introduction
The term ‘alexithymia’, coined by Sifneos [1], [2], describes a set of affective and cognitive characteristics. They are believed to reflect deficits in the processing or regulation of emotions through mental processes [3]. As indicated by the Greek term, its most prominent feature is a marked difficulty in describing one's own feelings to others. Alexithymia was defined as a multifacet construct composed of the following conceptually distinct, yet logically related, salient features: (a) “difficulty identifying feelings and distinguishing between feelings and the bodily sensations of emotional arousal”, (b) “difficulty describing feelings to other people”, (c) “constricted imaginal processes as evidenced by a paucity of fantasies” and (d) “a stimulus bound, externally orientated cognitive style” [3, p29]. Yet still, there is the problem of an adequate factorial structure of the construct in self-report measures.
The Toronto Alexithymia Scale (TAS-26) [4] was introduced as a reliable and valid measure of the construct. After several revisions, the actual 20-item version (TAS-20) [5], [6] resulted. For this scale, a three-factor structure was proposed [5]: (F1) “Difficulty identifying feelings”, (F2) “Difficulty describing feelings” and (F3) “Externally oriented thinking”. Although the majority of the factor analytic studies about the TAS-20 seem to support the original three-factor solution, a closer review shows that there might be alternative factor structures. The results of studies using exploratory factor analyses (EFAs) varied. In three studies, the common three-factor solution was preferred [5], [7], [8]. In one study, a one-factor model was found [9], and as had already occurred with the two previous versions of the TAS, some researchers found a two-factor solution in various language versions where the items of F1 and F2 formed a common factor [10], [11], [12]. However, two of these studies [10], [11] were criticized by Taylor et al. [13] because of sample characteristics or divergent results of exploratory and confirmatory factor analyses (CFAs) (cf. Ref. [14]). Other researchers found a factor structure where “Externally oriented thinking” decomposed into two factors “Pragmatic thinking” and “Lack of subjective significance or importance of emotions” [10], [15], [16], [17], [18], [19] (cf. also Ref. [20]).
In addition to EFA, in a large number of studies, CFAs of the TAS-20 with structural equation modeling were conducted [5], [9], [10], [14], [18], [19], [21], [22], [23], [24], [25], [26], [27], [28], [29]. Most of these studies yielded an acceptable fit of the three-factor model established by Bagby et al. [5]. Only in 5 out of these 15 studies, the common three-factor model showed no acceptable fit [9], [10], [18], [27], [29]. However, the studies reported above had some limitations. The fit indices (Goodness of Fit Index [GFI], Adjusted Goodness of Fit Index [AGFI] and RMR) or the criteria for acceptable fit of these indices used in most of the cited studies with CFA had been criticized [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42]. Furthermore, competing models with two or three factors were only compared in few studies. Alternative models like those mentioned above [10], [16], [17], [18], [19] were tested in none of the studies, although they are empirically supported and might be equally plausible.
Taking all this together, many of the studies reviewed here support the original three-factor model [5] of the TAS-20. However, there are hints that the factor structure of the TAS-20 may vary across various studies, samples and language versions (cf. also Ref. [43]). The factor structure, however, is clearly an important issue regarding the multidimensionality of the alexithymia construct. The current study was intended to contribute to the clarification of the inconsistent findings concerning the factor structure of the TAS-20 reported above and to address the limitations of many of these studies. Thus, in this study, five competing factor models of the TAS-20 with one to four factors were tested for their fit with data from a clinical and a nonclinical sample. The models were compared concerning (a) the global fit, (b) the relationships among the TAS factors, (c) parameter estimates among the factors and (d) the reliability of the factors.
Section snippets
Subjects and procedure
The clinical sample consisted of 204 inpatients (59.3% women) of a large hospital for psychosomatic disorders and a clinic for substance abuse. Their diagnoses were primarily anxiety disorders, somatoform disorders, somatic diseases traditionally regarded as psychosomatic and alcohol abuse. The mean age of the patients was 47.1 years (S.D.=8.0) with a range from 23 to 63 years. Regarding the educational level, 56.1% of the patients had finished secondary school (Hauptschule), 31.2% had finished
Global fit of models
The global model fit indices for both samples are presented in Table 2. Using the combinational rule of SRMR≤0.11 and RMSEA≤0.06, the two-factor model (b) (ID/DE–ET), the three-factor model (c) (ID–DE–ET), the three-factor model (d) (ID/DE–PR–IM) and the four-factor model (e) (ID–DE–PR–IM) in the patient sample showed a good fit with the data. The SRMR met the predefined criterion in these models. Regarding the lower boundary of the 90% confidence interval of the RMSEA, the possibility cannot
Factor structure and model fit
The two-factor model (b) (ID/DE-ET), the three-factor models (c) (ID–DE–ET) and (d) (ID/DE–PR–IM) and the four-factor model (e) (ID–DE–PR–IM) showed a good global goodness-of-fit in the patient sample. In the normal adult sample, none of the models fit the data particularly well. Though the difference between the tested models was small, the four-factor model yielded the best fit in both samples and should be preferred on the basis of this criterion. This was confirmed by a significant χ2
Conclusions
When the TAS-20 is applied for individual diagnosis of alexithymia, the reliability and the conceptual clarity of the factor “externally oriented thinking” should be increased. Further, there is evidence that the factor structure of the TAS-20 may vary across samples. As a consequence, the factor structure may emerge as more or less differentiated. Whether factor structures different from the common three-factor structure are an exception in some mainly clinical populations or a common
Acknowledgements
The authors wish to thank Johanna Schams and Benedikt Reuter for their help in collecting parts of the data reported in this article. The support of the Rhön-Rehabilitationsklinik Bad Kissingen and the Saaletalklinik Bad Neustadt is greatly appreciated. This paper was prepared with the assistance of the members of the CERE Group and the support of the Maison des Sciences de l'Homme, Paris.
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