Signature
d = U_0 - U_1; Q_loss = d * dur
| Inputs | Definition | Unit |
|---|---|---|
U_0 | Utility of comparable people without the harm, from the same instrument and value set | utility, 1 = full health |
U_1 | Utility of people with the harm | utility, 1 = full health |
dur | Time the harm lasts | years |
d | Fall in utility caused by the harm, positive for a loss | utility points |
|---|---|---|
Q_loss | Decrement times duration, undiscounted | QALYs |
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
Disutility and QALY loss from named utility cells
With BaseUtil, HarmUtil and HarmYears named, the formulas return the decrement and the QALY loss, held in Disut and QALYLoss.
=BaseUtil-HarmUtil; =Disut*HarmYears
Assumptions
Decrement measured from the baseline it is applied to
U_0 and U_1 come from the same dataset, instrument and value set; moving a decrement measured from full health onto a disease state assumes the same absolute effect at any level of health.
Constant decrement over the harm's duration without discounting
The decrement applies unchanged for dur years and the loss is undiscounted; with discounting or a changing decrement, HE-FM-QALY-001 applies period by period.
Worked examples
Decrement for condition A from a baseline utility of 0.80
People of about 65 with neither condition have mean utility 0.80 and those with condition A 0.70, so d_A = 0.10, as in the article; over five years the loss is 0.50 QALYs (computed here for illustration).
U_0 = 0.8; U_1 = 0.7; dur = 5; d = 0.1; Q_loss = 0.5
Decrement for condition B from a baseline utility of 0.80
With 0.60 for condition B alone, d_B = 0.20, as in the article, and the loss over five years is 1.00 QALY (computed here for illustration).
U_0 = 0.8; U_1 = 0.6; dur = 5; d = 0.2; Q_loss = 1
Common errors
Subtracting a decrement the baseline utility already contains
TSD 12 warns that decrements for grade 1 to 2 adverse events need care because the cohort behind the main utilities may already include patients who had them; utilities collected during treatment can likewise already reflect treatment burden.
Ignoring treatment process decrements over long horizons
Brennan and Dixon's review found process utility values for different drug delivery methods from 0.02 to 0.27; a decrement of 0.02 lasting as long as a ten-year treatment is 0.2 QALYs (computed here for illustration).
Sources
TSD 12 on adverse event decrements and double counting
Ara R, Wailoo A. NICE DSU Technical Support Document 12: The use of health state utility values in decision models. Sheffield: Decision Support Unit, ScHARR, University of Sheffield; July 2011 (full text read). Section 3.2.1 (Adverse events; TSD 12 numbers two subsections 3.2.1), p. 14: it is important to distinguish acute events from chronic sequelae and to include decrements for grade 3 to 4 adverse events; care is required so that decrements for grade 1 to 2 events are not double counted, as the cohort used for the main utilities may have included patients who had them.
Process utility values for drug delivery methods
Brennan VK, Dixon S. Incorporating process utility into quality adjusted life years: a systematic review of empirical studies. PharmacoEconomics. 2013;31(8):677-691. doi:10.1007/s40273-013-0066-1 (abstract read). Abstract (Results): measures of process utility for different drug delivery methods ranged from 0.02 to 0.27.
Canonical Identity
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