Live long, live well: quantifying the health of heterogeneous populations.

Various health, quality, utility and disability adjusted life years or life expectancy (HALY, QALY, DALY; HALE, QALE, DALE) measures have become gold standards for defining outcomes in technology evaluation, population health monitoring, and other evaluative efforts. As such, the analytical framework within which these measures are used for descriptive and evaluative purposes should be theoretically consistent and statistically rigorous. For instance, widely accepted definitions of cost-effectiveness ratios and other technology evaluation criteria that are based on expectations of the respective cost and outcome measures must, as such, be defined in terms of expected HALYs or QALYs. Similarly, measures like HALEs or QALEs used for population health monitoring are typically concerned with population expectations of such measures (or their corresponding totals). This paper demonstrates that estimation of such expectations necessitates consideration of the population variation in, and covariation between, quality and longevity. From the perspective of several different environments characterizing such heterogeneity, quantification or estimation of measures like QALYs is reconsidered. An empirical example of the central issues is provided by means of an analysis of the years of healthy life (YHL) measure drawn from the US National Health Interview Survey. Copyright 2001 John Wiley & Sons, Ltd.