Reliability and Validity of the Geriatric Depression Scale in Italian Subjects with Parkinson's Disease.

Introduction: The Geriatric Depression Scale (GDS) is commonly used to assess depressive symptoms, but its psychometric properties have never been examined in Italian people with Parkinson's disease (PD). The aim of this study was to study the reliability and validity of the Italian version of the GDS in a sample of PD patients.

Methods: The GDS was administered to 74 patients with PD in order to study its internal consistency, test-retest reliability, construct, and discriminant validity.

Results: The internal consistency of GDS was excellent ( α  = 0.903), as well as the test-retest reliability (ICC = 0.941 [95% CI: 0.886-0.970]). GDS showed a strong correlation with instruments related to the depression ( ρ  = 0.880) in PD ( ρ  = 0.712) and a weak correlation with generic measurement instruments (-0.320 <  ρ  <-0.217). An area under the curve of 0.892 (95% CI 0.809-0.975) indicated a moderate capability to discriminate depressed patients to nondepressed patient, with a cutoff value between 15 and 16 points that predicts depression (sensitivity = 87%; specificity = 82%).

Conclusion: The GDS is a reliable and valid tool in a sample of Italian PD subjects; this scale can be used in clinical and research contexts.