Signature
G = (U_A - U_AB) * dur; CPQ = C_case / G
| Inputs | Definition | Unit |
|---|---|---|
U_A | Utility of people with condition A alone | utility |
U_AB | Combined utility from the additive, multiplicative or minimum rule (HE-FM-DISU-002) | utility |
dur | Duration of condition B had it occurred | years |
C_case | Incremental cost of the intervention per case of B prevented | pounds |
G | Undiscounted QALYs gained by one person who avoids condition B | QALYs |
|---|---|---|
CPQ | Cost per case avoided divided by the QALY gain per case | pounds per QALY |
Function
Utility decrements, their QALY losses and the rules for combining them on a stated baseline
Expresses a harm such as an adverse event, a second chronic condition or an unpleasant treatment as a fall in utility from a stated baseline, turns it into lost QALYs over the harm's duration, and estimates the utility of people with two conditions from single-condition data by the additive, multiplicative or minimum rule of NICE DSU TSD 12. QALYs from periods of constant utility are HE-FM-QALY-001 and the expected QALY loss from adverse events HE-FM-AER-006. Notation follows the Disutility article.
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Implementations
Excel
QALY gain and cost per QALY from named cells
With OneCondUtil, BothUtil, AvoidYears and CaseCost named, the formulas return the QALY gain per case avoided and the cost per QALY, held in QALYGain and CostPerQALY.
=(OneCondUtil-BothUtil)*AvoidYears; =CaseCost/QALYGain
Assumptions
Avoided condition would have started at once and lasted the full period
Each avoided case of B would otherwise have started at the outset and lasted dur years, nobody dies and gains are undiscounted, as in the article's example.
Worked examples
Gain per case of B avoided under the additive rule
With U_A = 0.70 and the additive combined utility 0.50 over five years, the gain is 1.00 QALY and the cost per QALY at 20,000 pounds per case is 20,000 pounds, as in the article.
U_A = 0.7; U_AB = 0.5; dur = 5; C_case = 20000; G = 1; CPQ = 20000
Gain per case of B avoided under the multiplicative rule
The multiplicative combined utility of 0.525 gives a gain of 0.875 QALYs and a cost per QALY of about 22,857 pounds, as in the article.
U_A = 0.7; U_AB = 0.525; dur = 5; C_case = 20000; G = 0.875; CPQ = 22857.14
Gain per case of B avoided under the minimum rule
The minimum rule's 0.60 gives a gain of 0.50 QALYs and a cost per QALY of 40,000 pounds, above an illustrative threshold of 25,000 pounds that the other two rules meet, as in the article.
U_A = 0.7; U_AB = 0.6; dur = 5; C_case = 20000; G = 0.5; CPQ = 40000
Common errors
Crediting the avoided condition with a return to the baseline utility
A person who avoids B still has A, so the gain runs from the combined utility to 0.70, not to the baseline of 0.80; taking 0.80 overstates the additive gain from 1.00 to 1.50 QALYs (computed here for illustration).
Sources
PMG36 on documenting utility adjustments for comorbidities
National Institute for Health and Care Excellence. NICE technology appraisal and highly specialised technologies guidance: the manual (PMG36). London: NICE; 2022, last updated 31 March 2026 (full text of chapter 4 read). Section 4.3.7: adjustments to utility values may be needed for age or comorbidities, a multiplicative approach is generally preferred, and the methods used for adjusting utility values should be clearly documented.
Canonical Identity
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