Test-retest reliability and minimal detectable change of the Beck Depression Inventory and the Taiwan Geriatric Depression Scale in patients with Parkinson's disease.

The test-retest reliabilities of the BDI-II and the TGDS are high. The MDCs of both measures are acceptable to nearly excellent in people with PD. These findings imply that the BDI-II and the TGDS are suitable for use in a research context and in clinical settings to detect real change in a single subject.