The Geriatric Depression Scale should be shortened: results of Rasch analysis

Abstract

The purpose of this study was to examine the unidimensionality, item fit, redundancy and differential item functioning (DIF) of the 15-item version of the Geriatric Depression Scale (GDS) in a community sample of 300 Hong Kong Chinese patients with pneumoconiosis. Participants were randomly selected from the case register of the Pneumoconiosis Compensation Fund Board of Hong Kong. A trained research assistant administered the GDS to all participants. A psychiatrist, who was blind to the GDS scores, conducted a structured clinical interview to diagnose depressive disorders according to the Diagnostic and Statistical Manual for Mental Disorders, Version IV (DSM-IV) criteria. Of the 300 participants, 37 (12.3%) had a DSM-IV diagnosis of depressive disorders. Eleven out of 15 items (73.3%) had INFIT/OUTFIT statistics between 0.7-1.3. Abbreviated versions were created by removal of misfit and redundant items resulting in similar overall performance as the original 15-item GDS. None of the items had significant DIF for age, level of education and cognitive impairment. Although the GDS was overall unidimensional, there was evidence of item redundancy indicating that a shortened version would be as adequate as the original version.