Developing utilities: Quantifying quality of life for stages of Alzheimer's Disease as measured by the Clinical Dementia Rating

The objective was to develop utilities for stages of Alzheimer's disease as defined by the Clinical Dementia Rating. Utilities are ratings of preferences for a state of health which can serve as an indicator of Quality of Life (QoL). To determine if reliable utilities could be developed, we examined utility ratings for mild and severe dementia using Visual Analog scales and Time Trade-Off techniques. We examined these ratings across a range of rater characteristics. Experts in dementia research and graduate students in a School of Public Health rated a video tape of a patient with mild dementia (CDR=1) and severe dementia (CDR=3) and evaluated their QoL using a visual analog scale (VAS) and a time trade-off (TTO) technique. The VAS assessed global QoL and four components: Physical comfort, Happiness, Relationship to Family and friends, and Independence. The Tro technique attempted to assess the raters' ability to comprehend the task and included three questions to determine if the quantification was logical and internally consistent. Utility ratings were consistent with poorer ratings for more severe dementia and the TTO and VAS ratings were highly correlated for both expert and student raters. In general the TTO procedure yielded internally consistent and logical responses. Components of QoL were ranked comparably across raters and disease severity with the least reduction in QoL for physical comfort and the greatest reduction in independence. In general there was little correlation between demographic characteristics of the raters and utility ratings. These results demonstrate that QoL as measured by utility ratings for stages of AD defined by the CDR can be reliably evaluated, is internally consistent and comparable across different types of raters.