To identify the accuracy of depression rating scales as screening tools for detecting DpD and compare the diagnostic accuracy of different depression rating scales for detecting MDD among adults with Alzheimer's disease and related forms of dementia.

To examine factors that may impact on the accuracy of depression rating scales that are used to diagnose depression. We will examine the reference standard used for verification of DpD, baseline prevalence of DpD in the study population, age of the underlying study population, gender of participants, type of dementia (any-cause dementia versus Alzheimer’s disease), study setting (community or primary care setting, long-term care, tertiary care setting), and study country as potential sources of heterogeneity. We will also evaluate the effects of using different cut-points of individual depression rating scales on the diagnostic accuracy of the scales.