Table 2Description of the type and properties of distributions used in the PSA

ParameterType of distributionProperties of distributionParameters for the distribution
Proportion and probabilitiesBetaBounded on 0 – 1 interval. Derived from sample size, number of patients experiencing eventsα = events
β = sample size − α
CostGammaBounded at 0. Derived from mean and standard error.α = (mean/SEM)2
λ = mean/SEM2
TriangularThis distribution is used when no data other than the mean is available or when it is reported in the data source.Min = mean/2
Likeliest = mean
Max = mean + mean/2
Number of resources usedTriangularDerived from expert opinion or reported in data source.Min = minimum value
Likeliest = mean
Max = maximum value
Life expectancyTriangularReported in data source.Min = minimum value
Likeliest = mean
Max = maximum value
Utility decrementsGammaBounded at 0. Derived from mean and SE.α = (mean/SEM)2
λ = mean/SEM2
Relative riskLognormalBounded at 0. Derived from log (mean) and standard error.μ = ln(RR)
SD(μ) = (ln[UpperCI] − ln[lowerCI])/1.96*2

From: Appendix H, Cost-effectiveness analysis – Diagnosis of Pulmonary Embolism

Cover of Venous Thromboembolic Diseases
Venous Thromboembolic Diseases: The Management of Venous Thromboembolic Diseases and the Role of Thrombophilia Testing [Internet].
NICE Clinical Guidelines, No. 144.
National Clinical Guideline Centre (UK).
Copyright © 2012, National Clinical Guideline Centre.

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