Signature
w = 1 + 0.2 * ((AS >= 12) or (PS >= 0.85)) + 0.5 * ((AS >= 18) or (PS >= 0.95))
| Inputs | Definition | Unit |
|---|---|---|
AS | Absolute QALY shortfall under current care | discounted QALYs per person |
PS | Proportional QALY shortfall under current care | proportion |
w | Weight applied to the incremental QALYs of the new technology | multiplier, 1, 1.2 or 1.7 |
|---|
Function
Severity shortfall function
Maps the remaining discounted QALYs expected for an age- and sex-matched general population, and for people with the condition under current NHS care, to absolute and proportional QALY shortfall. NICE uses whichever measure implies greater severity to set a weight on the incremental QALYs of a new technology.
Implementations
Excel
Severity weight in one cell
With absolute and proportional shortfall in AbsShortfall and PropShortfall, Excel returns the weight from table 6.1 of PMG36.
=IF(OR(AbsShortfall>=18,PropShortfall>=0.95),1.7,IF(OR(AbsShortfall>=12,PropShortfall>=0.85),1.2,1))
Assumptions
Scope of the severity weight and judgement near cut-offs
The weight applies in technology appraisals. PMG36 does not apply it to highly specialised technologies, has not initially applied it to technology appraisals of HealthTech and considers it unlikely to be relevant in diagnostics. Shortfall estimates are uncertain, and the DSU guide notes that judgement is needed when an estimate lies close to a cut-off.
Weight on the QALY gain only
The weight multiplies the incremental QALYs of the technology, not the health forgone elsewhere, so a weight of 1.7 is equivalent to judging the unweighted ICER against £42,500 to £59,500 rather than £25,000 to £35,000. PMG36 asks for net health benefit at £25,000 and £35,000 per QALY both with and without the weight.
Worked examples
Weight in the DSU hypothetical case
Absolute shortfall of 5.93 and proportional shortfall of 0.50 are below both lower cut-offs, so the weight is 1.
AS = 5.93; PS = 0.50; w = 1
Absolute shortfall decides the weight
Absolute shortfall of 18.5 reaches the top band while proportional shortfall of 0.925 reaches only the middle band. The more severe measure applies, so the weight is 1.7, as in the article.
AS = 18.5; PS = 0.925; w = 1.7
Proportional shortfall on the cut-off
An older population with absolute shortfall of 9 and proportional shortfall of exactly 0.85 falls on the lower cut-off, and the higher band applies, giving a weight of 1.2. The figures are illustrative.
AS = 9; PS = 0.85; w = 1.2
Common errors
Taking the weight from one measure only
Checking only proportional shortfall gives a weight of 1.2 in the young-population example, where absolute shortfall of 18.5 gives 1.7. Both measures are assessed and the higher weight is used.
Applying the weight to total QALYs
The weight multiplies the incremental QALYs of the new technology over current care, not the total QALYs that patients would have anyway.
Sources
NICE QALY weightings for severity
National Institute for Health and Care Excellence. NICE technology appraisal and highly specialised technologies guidance: the manual (PMG36). Published 31 January 2022, last updated 31 March 2026. Chapter 6 Committee recommendations, section 6.2.18 and table 6.1 (weights of 1, 1.2 and 1.7; proportional shortfall cut-offs 0.85 and 0.95; absolute shortfall cut-offs 12 and 18; whichever implies greater severity; values on a cut-off take the higher level), sections 6.2.12, 6.2.19 and 6.2.20 (scope) and section 6.3.2 (net health benefit with and without the QALY weighting).
Weights applied to incremental QALYs
Wailoo A. NICE DSU Technical Support Document 23: A guide to calculating severity shortfall for NICE evaluations. Sheffield: Decision Support Unit, ScHARR, University of Sheffield; January 2024, updated September 2026. Section 1 (weights are applied to incremental QALYs and the definition giving the highest weight is used) and section 6 (judgement when estimates are close to a threshold).
Canonical Identity
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