Measurement equivalence of the Toronto Structured Interview for Alexithymia across language, gender, and clinical status

The Toronto Structured Interview for Alexithymia (TSIA) has been translated into Dutch, German, and Italian and validated in clinical and nonclinical populations. In order to make valid comparisons across different population groups, it is important to establish measurement equivalence across variables such as language, gender, and clinical status. Our objective in this study was to establish measurement equivalence in relation to language (English, Dutch, German, and Italian), gender, and clinical status (non-clinical, psychiatric, and medical) using differential item functioning (DIF). The sample was composed of 842 adults representing the four language groups, all of whom had undergone the TSIA assessment as part of several earlier studies. Ordinal Logistic Regression was employed to explore DIF of the TSIA items. Although several items were found to exhibit DIF for language, gender, or clinical status, all of these effects were within an acceptable range. These findings provide support for the measurement equivalence of the TSIA, and allow researchers to reliably compare results from studies using the TSIA across the four language groups, gender, and clinical status.