The Global Burden of Disease (GBD) study uses Disability-Adjusted Life Years (DALYs) as its primary metric. A DALY is calculated as:

• A Quality-Adjusted Life Years (QALYs) subtracted from total life expectancy
• B Years of Life Lost (YLL) + Years Lived with Disability (YLD) ✓
• C Years of premature death × disability weight
• D Life expectancy − healthy life expectancy (HALE)

Explanation

DALY = YLL + YLD, where YLL = number of deaths × standard life expectancy at age of death (years of life lost to premature death), and YLD = prevalence × disability weight × duration of illness (years lived with disability). One DALY = one lost year of healthy life. The GBD standard uses theoretical minimum risk life tables based on highest observed national life expectancy. DALYs allow comparison of disease burden across diverse conditions—communicable, NCD, and injuries. QALYs are used in cost-effectiveness analysis (gained healthy years) and are conceptually the inverse of DALYs.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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