The Disability-Adjusted Life Year (DALY) is composed of two components. Which formula correctly represents the DALY?
- A DALY = Years of Life Lost (YLL) + Years Lived with Disability (YLD) ✓
- B DALY = Years Lived with Disability (YLD) − Years of Life Lost (YLL)
- C DALY = Quality-Adjusted Life Years (QALY) + Years of Life Lost (YLL)
- D DALY = Healthy life expectancy (HALE) − Observed life expectancy
Correct answer: A. DALY = Years of Life Lost (YLL) + Years Lived with Disability (YLD)
Explanation
DALY = YLL + YLD. Years of Life Lost (YLL) measures premature mortality by comparing actual age at death with standard life expectancy; Years Lived with Disability (YLD) measures time lived in states of less than full health, weighted by disability severity. One DALY represents one year of healthy life lost. DALY is a burden-of-disease metric used by WHO's Global Burden of Disease study; unlike QALY (which measures benefit), DALYs measure loss — a lower DALY burden indicates better health.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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