The State-Trait Anxiety Inventory: does it measure anxiety or depression?

Introduction: An Italian 21-item unidimensional self-report scale of depression, named TDI (Balsamo, 2006), has been developed. It was based on the basis of diagnostic criteria for Major Depression Episode of DSM-IV-TR (2000), using item-response theory, specifically a modified version of the Rasch one-parameter modelling (Rasch, 1960-1980), proposed by Andrich (1988). Aims and Method: The objectives were to provide a contribution to validation and standardization of the TDI. The samples consisted of 493 Italian healthy subjects and 768 Italian outpatients with various psychiatric diagnosis. We administered the TDI, the Beck Depression Inventory-II (BDI-II; Beck, Steer e Brown, 1996) and the State-Trait Anxiety Inventory (STAI; Spielberger, 1991). Results: We calculated correlations between TDI total score and subjects’ age and sex. To estimate the convergent and discriminant validity of the TDI, we calculated correlations between TDI total score and BDI-II and STAI total scores. Discussion and Conclusions: The TDI is a 21-item unidimensional self-report scale of depression, which seems to catch the nucleus of depressive symptomatology. It has some advantages, as: 1. construction via Rasch analysis, which guarantees ordered sequence of the thresholds of each of the21 items; 2. calculation of the total score from the 21 items by summing of the response categories to polithomous items; 3. no impact of gender bias; 4. control of response sets; 5. good psychometric characteristics; 6.high sensitivity and specificity. It could be a valid screening instrument in that it sensitively discriminates between outpatients and normals.