In health care the reimbursement of medical providers is an important topic and can influence the overall outcome. We present the agent-based GAP-DRG model, which allows a comparison of reimbursement schemes in outpatient care. It models patients and medical providers as agents. In the simulation patients develop medical problems (i.e., diseases) and a need for medical services. This leads to utilization of medical providers. The reimbursement system receives information on the patients' visits

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... via its generic interface, which facilitates an easy replacement. We describe the assumptions of the model in detail and show how it makes extensive use of available Austrian routine care data for its parameterization. The model design is optimized for utilizing as much of these data as possible. However, many assumptions have to be simplifications. Further work and detailed comparisons with health care data will provide insight on which assumptions are valid descriptions of the real process. 2299 978-1-4799-2076-1/13/$31.00 ©2013 IEEE Einzinger, Popper, Pfeffer, Jung, Endel, and Breitenecker data, sick-leaves and hospital stays. The model construction was part of the "General Approach for Patient-oriented Ambulant Diagnosis Related Groups" (GAP-DRG) project (Endel 2011). One particular objective of the project was the analysis of DRG-like reimbursement schemes. Fetter et al. (1980) developed the original DRG system for the inpatient sector. Also in the 1980s, the first systems for ambulatory care were introduced (Fetter et al. 1984) . However, in the outpatient sector it is difficult to assign unique diagnoses to visits, and patients can have long or even chronic episodes of disease (Rogerson 1983) . The approach in the project was that episodes last for one quarter of a year, and those diagnoses for which a patient receives medical services during a quarter contribute to his or her classification. The general idea of the model is that reimbursement is the result of patients consuming medical services from medical providers because of their medical problems (i.e., diseases). It roughly follows the proposed structure of Krol and Reich (1999) , which is object-oriented and also contains the classes medical provider and patient. Figure 1 shows the general idea of the model diagrammatically and emphasizes that different reimbursement systems could be the basis for reimbursement. The general idea translates to two types of agents, the patients and the medical providers. The behavior in the model splits into five modules: