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VIH.pdf - Volume 12 • Supplement 1 • 2009 VA L U E I N H E...

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QALYs: The BasicsMilton C. Weinstein, PhD,1George Torrance, PhD,2Alistair McGuire, PhD31Harvard School of Public Health, Boston, MA, USA;2McMaster University, Hamilton, ON, Canada;3London School of Economics, London,UKKeywords:quality-adjusted life-year, cost-effectiveness analysis, preference, utility, standard gamble, time trade-off, taxonomy, theory.The FactsThe aim of this article is to review the concept of the quality-adjusted life-year (QALY), a widely used measure of healthimprovement that is used to guide health-care resource allocationdecisions. The QALY was originally developed as a measure ofhealth effectiveness for cost-effectiveness analysis, a methodintended to aid decision-makers charged with allocating scarceresources across competing health-care programs [1–3]. We referto this original concept of the QALY, as defined in the earlyliterature, as the “conventional” QALY, recognizing that alter-native conceptual models have been proposed, including but notlimited to so-called “equity-weighted” QALYs. The US Panel onCost-Effectiveness in Health and Medicine [4] and the NationalInstitute of Health and Clinical Excellence (NICE) in Britain haveboth endorsed the conventional QALY for their “reference case,”i.e., a standardized methodological approach to promote com-parability in cost-effectiveness analyses of different health-careinterventions.In using QALYs, we assume that a major objective of decision-makers is to maximize health or health improvement across thepopulation subject to resource constraints. The use of QALYsfurther assumes that health or health improvement can be mea-sured or valued based on amounts of time spent in various healthstates. The conventional QALY is therefore a valuation of healthbenefit. We note, however, that decision-makers may also haveother objectives such as equity, fairness, and political goals, all ofwhich currently must be handled outside theconventionalSpecialIssue [5] addresses some of these variations on the conventionalQALY. The QALY was not initially developed to aid individualpatient decision-making, although its use has sometimes beenextended into clinical decision analyses for this purpose.The core concept of the conventional QALY is grounded indecision science and expected utility theory. The basic constructis that individuals move through health states over time and thateach health state has a value attached to it. Health, which is whatwe are seeking to maximize, is defined as the value-weightedtime—life-years weighted by their quality—accumulated over therelevant time horizon to yield QALYs. Health states must bevalued on a scale where the value of being dead must be 0,because the absence of life is considered to be worth 0 QALYs. Byconvention, the upper end of the scale is defined as perfect health,with a value of 1. To permit aggregation of QALY changes, thevalue scale should have interval scale properties such that, forexample, a gain from 0.2 to 0.4 is equally valuable as a gain from0.6 to 0.8. States worse than dead can exist and they would havea negative value and subtract from the number of QALYs. Theseconditions, along with an assumption of risk neutrality overlife-years, are sufficient to ensure that the QALY is a usefulrepresentation of health state preferences.

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Term
Fall
Professor
terrence brown
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