The Toronto Alexithymia Scale is a measure of deficiency in understanding, processing, or describing emotions.
It was developed in 1986 and later revised, removing some of the items.
The current version has twenty statements rated on a five-point Likert scale.
The reliability and validity of the TAS-20 was established by a series of articles by Bagby and colleagues (1994).
Bagby, R.M., Parker, J.D.A. & Taylor, G.J. (1994) The Twenty-Item Toronto Alexithymia Scale—I. Item Selection and Cross-Validation of the Factor Structure. Journal of Psychosomatic Research. 38(1), pp.23-32.