Disability-Adjusted Life Year (DALY) is a composite health metric. Which formula correctly represents DALYs?
- A DALYs = Years of Life Lost (YLL) × Disability Weight
- B DALYs = Years of Life Lost (YLL) + Years Lived with Disability (YLD) ✓
- C DALYs = Life Expectancy − Healthy Life Expectancy (HALE)
- D DALYs = (Incidence × Disability Weight) ÷ Mortality Rate
Correct answer: B. DALYs = Years of Life Lost (YLL) + Years Lived with Disability (YLD)
Explanation
DALYs = YLL + YLD, where YLL measures years of life lost to premature death (deaths before a standard reference life expectancy) and YLD measures years lived with disability (incidence × duration × disability weight, where disability weight ranges 0–1). One DALY represents one year of healthy life lost. The formula captures both the fatal and non-fatal burden of disease. HALE (option C) is a different metric measuring healthy life expectancy. Disability weight alone is not multiplied by YLL.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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