Health state descriptions for Canadians
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By Kellie A. Langlois, Andriy V. Samokhvalov, Jürgen Rehm, Selene T. Spence, Sarah Connor Gorber
This document provides standardized descriptions for the main health states associated with the progression and treatment of a disease. These descriptions are the first step in measuring how living with a disease and its treatment affects health-related quality of life in terms of physical, mental, and social well-being.
Underlying this approach is a new tool to measure functional health. Among other attributes, pain, limitations to physical functioning, or anxiety can limit an individual's ability to participate in day-to-day activities. We classify these using the Classification and Measurement System of Functional Health (CLAMES), with eleven such attributes that span physical, social and mental well-being. For each attribute, there are four or five levels ranging in severity from no limitations in the attribute to severe limitations. Level 1, for instance, represents no limitations; for the attribute describing pain and discomfort it would read "generally free of pain and discomfort." The table that follows (Classification and Measurement System of Functional Health (CLAMES)) shows the complete list of levels for each attribute.
For each health state, we describe a "typical" case, based on a combination of literature review and expert consultation. Although every individual's experience of a given disease will be unique, creating these general descriptions is necessary for measuring health at the population level.
The first step in this process involves conducting an extensive review of the literature on a particular disease, in order to collect information on the main types of the disease, the usual progression, symptoms, and resulting functional limitations, and typical treatment options and their effects.
This evidence is then synthesized in order to create the health state classifications. Essentially, each health state is classified according to 11 CLAMES attributes to represent its overall consequences for functional health. In this way, a large amount of information on the typical experience of a disease is condensed into a more manageable form, which facilitates measurement of the impact of the disease on the population. Next, in order to ensure their clinical accuracy, the health state descriptions and classifications are reviewed by medical experts and revised accordingly.
The classifications are used to elicit preference scores from panels of Canadians based on techniques grounded in utility theory. Preference scores, which indicate the relative preference for a health state compared with full health, help us understand how Canadians view the various aspects of functional health. Along with data on incidence and duration, preference scores contribute to estimates of the impact on the Canadian population of both disease and risk factors that contribute to them.
Measured in terms of years of life lost to premature mortality and year-equivalents of reduced functioning due to the disease, these estimates allow us to determine how many years of life—and how many years of healthy living—are lost due to specific diseases and risk factors. They provide answers to questions such as "what would be the impact of reducing obesity on the health of Canadians?" both in terms of lives saved and in terms of increased health over their lifespan.
For further details on the Population Health Impact of Disease in Canada (PHI) research program, the process of creating the health state descriptions and classifications, and the development of population estimates to which they contribute, please consult the PHI website at http://www.phac-aspc.gc.ca/phi-isp/index.html.
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