Topic

QALYs, DALYs and summary measures

Summary measures combine length of life and quality of life into a single number. The quality-adjusted life year weights each year lived by a utility value, while the disability-adjusted life year adds years of life lost to years lived with disability. Health expectancies such as active life expectancy describe population health in a similar way.

Concepts in this topic

• Active Life ExpectancyActive life expectancy (ALE) is the average number of years a person of a given age can expect to live free of dependency in activities of daily living.
• DALY Calculation MethodThe methodology used to compute disability-adjusted life years, combining years of life lost to premature death with years lived with disability, weighted by severity.
• Disability WeightA disability weight is a value from 0 (full health) to 1 (equivalent to death) rating health loss in a non-fatal state, used to calculate YLDs and DALYs.
• Disability-Adjusted Life YearA disability-adjusted life year, or DALY, measures health loss by combining years of life lost because of premature death with years lived with disability.
• Health-Adjusted Life YearA general term for outcome measures, including the QALY and DALY, combining length of life with a weighting for quality or disability into one unit.
• Health-Related Quality of LifeA multidimensional concept covering the physical, psychological, and social aspects of wellbeing affected by a person's health status or its treatment.
• Healthy Year EquivalentAn alternative to the QALY deriving its valuations directly from a sequence of health states over a lifetime, rather than combining separate utility values.
• QALY Calculation MethodThe process of computing quality-adjusted life years by multiplying time spent in a health state by its utility value, then summing across states.
• QALY GainThe increase in quality-adjusted life years attributable to an intervention, the difference between the QALYs expected under it and its comparator.
• Quality-Adjusted Life Year (QALY)A quality-adjusted life year (QALY) combines length and quality of life in one measure: a year in full health counts as one QALY and death counts as zero.
• Quality-Adjusted Time Without SymptomsA quality-weighted survival measure that partitions time into toxicity, time without defined symptoms or toxicity, and time after disease progression, then sums each duration multiplied by its state-specific weight.
• Time Without Symptoms of ProgressionA phase within the Q-TWiST framework covering the period free of significant treatment toxicity or disease progression symptoms, typically weighted highest.
• Years Lived with DisabilityYears lived with disability (YLDs) measure non-fatal health loss, usually as prevalence times disability weight; adding years of life lost gives the DALY.