title: Modeling rheumatoid arthritis using different techniques - a review of model construction and results.
abstract: BACKGROUND
  Rheumatoid arthritis (RA) is a chronic, inflammatory disease with severe effects on the functional ability of patients. Due to the prevalence of 0.5 to 1.0 percent in western countries, new treatment options are a major concern for decision makers with regard to their budget impact. In this context, cost-effectiveness analyses are a helpful tool to evaluate new treatment options for reimbursement schemes.
  
  
  OBJECTIVE
  To analyze and compare decision analytic modeling techniques and to explore their use in RA with regard to their advantages and shortcomings.
  
  
  METHODS
  A systematic literature review was conducted in PubMED and 58 studies reporting health economics decision models were analyzed with regard to the modeling technique used.
  
  
  RESULTS
  From the 58 reviewed publications, we found 13 reporting decision tree-analysis, 25 (cohort) Markov models, 13 publications on individual sampling methods (ISM) and seven discrete event simulations (DES). Thereby 26 studies were identified as presenting independently developed models and 32 models as adoptions. The modeling techniques used were found to differ in their complexity and in the number of treatment options compared. Methodological features are presented in the article and a comprehensive overview of the cost-effectiveness estimates is given in Additional files 1 and 2.
  
  
  CONCLUSIONS
  When compared to the other modeling techniques, ISM and DES have advantages in the coverage of patient heterogeneity and, additionally, DES is capable to model more complex treatment sequences and competing risks in RA-patients. Nevertheless, the availability of sufficient data is necessary to avoid assumptions in ISM and DES exercises, thereby enabling biased results. Due to the different settings, time frames and interventions in the reviewed publications, no direct comparison of modeling techniques was applicable. The results from other indications suggest that incremental cost-effective ratios (ICERs) do not differ significantly between Markov and DES models, but DES is able to report more outcome parameters.
  
  
  CONCLUSIONS
  Given a sufficient data supply, DES is the modeling technique of choice when modeling cost-effectiveness in RA. Otherwise transparency on the data inputs is crucial for valid results and to inform decision makers about possible biases. With regard to ICERs, Markov models might provide similar estimates as more advanced modeling techniques.
authors.affiliation: Bielefeld University, Faculty of Public Health, Universitätstr. 25, 33615, Bielefeld, Germany, stefan.scholz@uni-bielefeld.de.
authors.forename: Stefan
authors.initials: S
authors.lastname: Scholz
authors.forename: Thomas
authors.initials: T
authors.lastname: Mittendorf