Factorial validity and measurement invariance of the 20-item Toronto Alexithymia Scale in clinical and nonclinical samples.

The most widely used instrument to measure alexithymia is the 20-item Toronto Alexithymia Scale (TAS-20). However, different factor structures have been found in different languages. This study tests six published factor models and metric invariance across clinical and nonclinical samples. It also investigated whether there is a method effect of the negatively keyed items. Second-order models with alexithymia as a higher order factor are tested. Confirmatory factor analyses showed that the original factor model with three factors-difficulty identifying feelings (DIF); difficulty describing feelings (DDF) and externally oriented thinking (EOT)-is the best fitting model. Partial measurement invariance across samples was illustrated but requires further study. A weakness of the model is the low internal consistency of the third factor. Because models with a method factor had a better fit, future reconsideration of the negatively formulated items seems necessary. No evidence was found for the second-order models.