Rasch analysis of the Geriatric Depression Scale-Short Form.

PURPOSE

The purpose of this study was to examine scale dimensionality, reliability, invariance, targeting, continuity, cutoff scores, and diagnostic use of the Geriatric Depression Scale-Short Form (GDS-SF) over time with a sample of 177 English-speaking U.S. elders.

DESIGN AND METHODS

An item response theory, Rasch analysis, was conducted with data from a larger study that implemented 3 interventions and collected data at 3 time points (prior to intervention, after intervention, and a year following the end of intervention).

RESULTS

A unidimensional structure was found in this study to adequately fit the data. There appears to be significant differential item functioning, with up to one third of the items indicating that the items have different meanings for different groups of participants. As a screening tool, the GDS-SF is more likely to discriminate between older adults who have a "moderate" level of depression than between those with mild depression and no diagnosed depression.

IMPLICATIONS

We would recommend that the GDS-SF not be used as the sole method of screening for depression but incorporated into other clinical knowledge related to the geriatric patient in question, given that not all items are equally functional. The GDS-SF may be less effective as a screening tool but could be better used to detect a change in moderate levels of depression. Clinicians may also benefit by identifying person responses that misfit. If an individual provides responses that are atypical, the person might be referred to provide a more in-depth assessment of mental health status.