Signature
Q_AE = sum_(k=1)^K [p_k * u_k * tau_k]
| Inputs | Definition | Unit |
|---|---|---|
p_k | Probability of an episode of adverse event type k over the period modelled | probability from 0 to 1 |
u_k | Reduction in utility while an episode of event type k lasts | utility on the 0 (dead) to 1 (full health) scale |
tau_k | Duration of one episode of event type k as a fraction of a year, for example 14/365 for two weeks | years |
Q_AE | Expected loss of quality-adjusted life years per patient from the adverse events included | QALYs per patient |
|---|
KNumber of adverse event types with a disutility, equal to the length of the p_k, u_k and tau_k lists (count)
Function
Adverse event rate to model input function
Maps the adverse event counts in a trial safety table, with their denominators of patients or person-time, to the probability of an event in one model cycle, and maps those probabilities to the expected adverse event cost and QALY loss per patient. The general rate and probability conversions are on the Transition Probability page (HE-FN-TP-001); the records here apply them to adverse event data and add the cost and QALY weighting.
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Implementations
Excel
Expected adverse event QALY loss with SUMPRODUCT
With the event probabilities in AEProbs, the disutilities in AEDisutilities and the episode durations in years in AEEpisodeYears, all ranges of the same size, Excel returns the expected QALY loss per patient.
=SUMPRODUCT(AEProbs,AEDisutilities,AEEpisodeYears)
Assumptions
Short-lived adverse events as one-off decrements
Each episode lowers utility for a limited time and then resolves. Events that cause death, long admissions or lasting disability are modelled as separate health states rather than as one-off decrements.
Health state utilities free of adverse event effects
The utilities of the health states in the model do not already reflect adverse effects. Craig and colleagues found that 53% of the HTA models that included utilities derived them from patients on treatment, so those values could already capture adverse effects.
Worked examples
Expected QALY loss from diarrhoea on the new drug
Illustrative figures: a utility decrement of 0.10 for 14 days is a loss of about 0.00384 QALYs per episode. With a probability of 0.18 the expected loss is about 0.00069 QALYs per patient.
p_k = [0.18]; u_k = [0.10]; tau_k = [0.038356]; K = 1; Q_AE = 0.00069
Expected QALY loss from diarrhoea on the comparator
With a probability of 0.08 the expected loss is about 0.00031 QALYs per patient. The difference of about 0.00038 QALYs is worth about £8 at an illustrative £20,000 per QALY, the figure used in the article (the NICE manual PMG36, as updated in March 2026, uses £25,000 to £35,000 per QALY). At either value it is small beside the £180 difference in adverse event costs.
p_k = [0.08]; u_k = [0.10]; tau_k = [0.038356]; K = 1; Q_AE = 0.00031
Common errors
Entering the adverse event duration in days
Multiplying the decrement of 0.10 by 14 days rather than by 14/365 of a year gives a loss of 1.4 QALYs per episode instead of about 0.00384, more than a year of full health for a two-week event.
Adding adverse event disutilities to on-treatment utilities
When the health state utilities were measured in patients on treatment, they may already include the effect of adverse events, and subtracting a separate disutility per event can count the same loss twice.
Sources
Utilities and adverse effects in HTA decision models
Craig D, McDaid C, Fonseca T, Stock C, Duffy S, Woolacott N. Are adverse effects incorporated in economic models? An initial review of current practice. Health Technology Assessment. 2009;13(62). Review of 80 NIHR HTA reports: 53% of the models that included utilities derived them from patients on treatment and could therefore be interpreted as capturing adverse effects.
Quality of life loss from adverse events in economic evaluation
Ghabri S, Dawoud D, Drummond M. Methods for including adverse events in economic evaluations: suggestions for improvement. Value in Health. 2024;27(7):936-942. Discusses estimating the quality of life loss from adverse events and impacts not adequately captured by current measures of health-related quality of life.
NICE table of decrements associated with adverse events
National Institute for Health and Care Excellence. NICE technology appraisal and highly specialised technologies guidance: the manual (PMG36). 2022, updated March 2026. Section 4.10.4, which asks for a table including QALYs by health state and the decrements associated with further interventions and adverse events.
Canonical Identity
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