Journal of affective disorders vol:22 issue:1-2 pages:54-64
The present study investigates the psychometric adequacy of a self-report inventory of depression (the QD2) with respect to the severity of depressive symptoms, within the framework of a unidimensional model of depressive states. Responses to the 52 QD2 items, by 481 subjects divided into four groups (depressed, psychiatric, somatic and control), were subjected to a Rasch analysis. Results show that 15 items (QSD(R1)) display a satisfactory goodness of fit for both items and persons, as defined by the Rasch model. This set of items, solely related to 'pure' depression, gives a measure of the severity of depression, free from anxiety symptoms. The discussion focuses upon the advantages of the Rasch model as compared to traditional tests. The Rasch 15-item solution should provide a parsimonious tool for future studies on the classification of depressive disorders.