The reliability and validity of the Collateral Source version of the Geriatric Depression Rating Scale administered by telephone

Objective. To prospectively evaluate the reliability and validity of the Collateral Source Geriatric Depression Scale (CS-GDS) administered by telephone (T-CS-GDS) in patients undergoing outpatient comprehensive geriatric assessment. Subjects. Eighty-three geriatric patients evaluated in a 1-year period at the outpatient Geriatric Assessment Center of the University of Nebraska Medical Center. Methods. The 30-item CS-GDS was completed by the collateral source of all patients on three occasions: by telephone several days before their assessment, face-to-face during their assessment visit and several days later, again by phone. During their assessment, all patients were evaluated by one of three geriatric psychiatrists who were blinded to CS-GDS results. The test-retest reliability of the T-CS-GDS was measured by comparing the results of the two phone interviews. The construct validity of the T-CS-GDS was estimated by comparing the results of the initial T-CS-GDS with the CS-GDS obtained during the comprehensive assessment. The criterion validity of the T-CS-GDS was estimated by comparing the results of the T-CS-GDS with the clinical diagnosis of depression assigned by the psychiatrists. Results. The individual items of the initial T-CS-GDS showed substantial concordance with the second T-CS-GDS (kappa range 0.41-0.8, mean = 0.61) and with the assessment GDS (kappa range 0.33-0.85, mean = 0.61). Twelve items showed evidence of bias when comparing the two T-CS-GDSs and four items when comparing the initial T-CS-GDS with the CS-GDS done during the assessment. The mean number of symptomatic responses was not significantly different for the T-CS-GDS vs assessment administration but did decline slightly when comparing the two T-CS-GDSs. ROC curve analysis showed good agreement between the clinical diagnosis and the T-CS-GDS. Conclusion. The CS-GDS appears to maintain its reliability and validity when administered via telephone and thus may be useful for a variety of epidemiologic and clinical purposes.