13 Research methods, statistics, critical review and evidence-based practice13.6 Economic analysis

13.6.4 QALYs and DALYs

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Written by Resident Doctor Committee · Published

The quality-adjusted life year

  • A quality-adjusted life year (QALY) is time lived weighted by the utility of the health state it is lived in, combining length and quality of life in one figure.

  • The QALY is the outcome unit of cost-utility analysis.

  • Utility is anchored at 1 for full health and 0 for death with no floor, so states judged worse than death take negative values and subtract QALYs.

Calculating QALYs

  • Total QALYs equal years lived multiplied by the utility for those years: one year at 0.6 gives 0.6 QALYs.

  • Incremental QALYs are the difference between the two options' lifetime QALY totals.

  • With survival unchanged and no discounting, this equals the utility difference multiplied by how long it lasts.

  • Raising utility from 0.6 to 0.8 for five years gives (0.8 - 0.6) x 5 = 1 additional QALY.

QALYs are the area under the quality of life curve: area A is the QALYs without intervention, and gold area B is the incremental QALYs the intervention adds through longer survival and better quality of life. Jmarchn, CC BY-SA 3.0, via Wikimedia Commons

Where utilities come from

The National Institute for Health and Care Excellence (NICE) prefers the EQ-5D, which rates mobility, self-care, usual activities, pain or discomfort, and anxiety or depression.

Method

What is offered

Utility

Time trade-off

Fewer years in full health instead of a longer period in the state

Indifference between ten years in the state and seven in full health gives 0.7

Standard gamble

The state for certain against a gamble between full health and immediate death

Probability of full health at indifference, so it includes attitude to risk

The disability-adjusted life year

The disability-adjusted life year (DALY) measures healthy life lost: DALYs = years of life lost (YLL) + years lived with disability (YLD).

Feature

QALY

DALY

Counts

Quality-adjusted life lived

Healthy life lost

Weight anchors

1 full health, 0 death

0 no loss, 1 loss equal to death

Direction

More is better

Fewer is better

Limitations in psychiatry

  • EQ-5D does not directly assess hallucinations, cognition or recovery, so it may miss meaningful change.

  • Extending life counts for less in someone with permanent impairment: five extra years at utility 0.5 give 2.5 QALYs, against 4.5 at 0.9.

Revision material for the MRCPsych examinations. Not clinical guidance, and not for use in patient care.