A critique and impact analysis of decision modeling assumptions.
BACKGROUND
A descriptive analysis of 4 modeling issues (inclusion of incident cases over a model time horizon, appropriate time horizon, parsimonious model structure, and the handling of age-specific subgroups) is presented. A case study model is analyzed to illustrate the quantitative impact of 3 of the issues.


RESULTS
In the case study model, alternative specifications of the modeling framework are shown to alter the estimated cost-effectiveness by large percentages. The combined effect of including incident cases and reduced follow-up yielded the highest divergence from the reference case results, by between 20% and 40%, depending on the age group. Reference case results of an age-weighted population were almost 14% different from the middle single age cohort.


CONCLUSIONS
The identified issues are all generalizable to a wide range of treatment areas and are, or should be, addressed by evaluative guidelines. The authors call for the continued development, dissemination, and application of guidelines for the conduct of economic evaluation in general and model-based economic evaluations in particular.
Karnon
Jonathan
J
School of Health and Related Research, University of Sheffield, Sheffield, UK. j.karnon@sheffield.ac.uk
Brennan
Alan
A
Akehurst
Ron
R
D000367:Age Factors; D000925:Anticoagulants / Q000191:economics / Q000627:therapeutic use; D003327:Coronary Disease / Q000191:economics / Q000517:prevention & control; D003362:Cost-Benefit Analysis; D003661:Decision Support Techniques; D006801:Humans; D017059:Models, Econometric; D017410:Practice Guidelines as Topic; D013997:Time Factors
D000925:Anticoagulants