Review of outcome measurement instruments in Alzheimer's disease drug trials: psychometric properties of global scales.

Abstract

The use of global outcome measures with strong psychometric properties in Alzheimer's disease (AD) drug trials is encouraged. This article focuses on Clinician Global Impression of Change scales, the Clinical Dementia Rating, and the Global Deterioration Scale to provide (1) a review of psychometric properties, (2) a critique of how these properties are assessed in the literature, and (3) a basis for evaluating, from the standpoint of psychometric properties, the appropriateness of using a given global scale in a drug trial. Reported reliability and validity estimates for the aforementioned scales range from fair to very good, but small sample sizes and/or inappropriate measures of correlation weaken the quality of the evidence. There is also a dearth of published information on responsiveness to change. Researchers planning AD drug trials should consider these issues, along with the interval between test administrations for test-retest reliability, to help select appropriate global outcome measurement instruments.