1. Sensitivity in Cost Effectiveness Analyses
Sensitivity of a CEA on prevention strategies against Neural Tube Defects using DPL software.
Radboud Duintjer Tebbens

2. Contents Objectives Problem Description The Model
Implementation and Deterministic Results
Sensitivity Analysis
Probabilistic Model
Conclusions
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Sensitivity in CEA's

3. Objectives Exploring the possibilities of DPL for sensitivity analyses
Getting familiar with Cost Effectiveness Analyses
How can sensitivity analyses on CEA’s be improved?
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4. Problem Description What is a Cost Effectiveness Analysis?
Analysis that compares health interventions using C/E ratio
C/E ratio = Incremental Cost/Incremental Effectiveness
= Incremental Cost / Incremental QALY’s
QALY: Quality-Adjusted Life Year
1 QALY = 1 year in full health
0 QALY = 1 year dead
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5. Problem Description (2)
The CEA on Neural Tube Defects (NTD’s) considers 5 health programs for prevention of NTD’s on newborns:
1. No Program (baseline)
2. Supplementation: education program to stimulate women aged to take Vitamin Supplements
3,4&5. Fortification with folic acid: a rule that forces food producers to fortify cereals with folic acid, 0.14 , 0.35 or 0.70 mg per 100g of cereals
The CEA on neural tube defects is described in the appendix of the book: Cost-effectiveness in Health and Medicine, M.R. Gold et. al, Oxford University Press 1996
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Sensitivity in CEA's

6. Problem Description (3)
Adverse Effect in Fortification Programs: intakes of more than 1.0 mg of folic acid can cause delayed diagnosis of vitamin B12 deficiency which can lead to neurological complications, mostly by elderly persons
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7. The Model Simple deterministic model that:
Calculates the number of babies born with NTD with each program
Calculates the number of Adverse Effects caused by any of the programs
Adds costs of the various programs and their health outcomes
Uses expert judgment outcomes to evaluate the number of QALY’s gained compared to the baseline case ‘no program’.
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8. The Model (2) Important Uncertain Parameters:
parameter value sensitivity range
QALY’s per NTD
Costs per NTD
QALY’s per Adverse Effect
Costs per Adverse Effect
pNTD
pNTD
pOAdvEff
pBegSupp
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9. Model (3)
pNTD0.4+ is the probability that a women aged who consumes at least 0.4 mg of folic acid daily will have an NTD affected pregnancy.
pNTD0.4+ is the probability that a women aged who consumes less than 0.4 mg of folic acid daily will have an NTD affected pregnancy.
The difference between these variable accounts for the number of prevented NTD’s by the health intervention.
pOAdveff, the probability that someone who is not a woman aged and who consumes more than 1.0 mg of folic acid daily, eventually quantifies the occurrence of neurological complications
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10. Implementation and Deterministic Results
Straightforward Influence Diagram with
1 Decision Node: Program
Many Value Nodes containing all model parameters
Objective function to be minimized:
Incremental C/E = Costs/QALY’s Gained
NB: I used Costs instead of Incremental Costs
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11. Implementation and Deterministic Results (2)
Program Costs(M$) QALY’s lost Incremental C/E
No Program
Suppl
Fort
Fort
Fort
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12. Sensitivity Analysis Univariate: Rainbow Diagrams or Tornado Diagrams
Many Univariate Sensitivity Analyses at once: Tornado Diagrams
Multivariate?
(See accompanying DPL file: NTDdeterm.da)
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13. Probabilistic Model Not conceptually very clear
Use of Risk Profiles and probability distributions, but very basic
No improvement for sensitivity visualization
(See accompanying DPL file: NTDprob.da)
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14. Conclusions
DPL is good for a first look at sensitivity of a model on its parameters.
First look at CEA on NTD prevention shows that the decision based on the C/E ratio is very little sensitive to most uncertain parameters, even though the cost and health outcomes are quite sensitive to them.
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15. Conclusions (2) Multivariate sensitivity analyses for CEA’s?
It would be interesting to look at uncertainty analysis for CEA’s, taking into consideration the (joint) probability distribution of the uncertain parameters (but is it necessary?)
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Sensitivity in CEA's