Creating common patients and evaluating indiviual results: Issues in indivual simulation for health policy analysis

The research direction in modeling complex, chronic conditions for health policy evaluation has been to incorporate individual heterogeneity. This detail makes our models more powerful and relevant. In implementing an individual simulation model of colorectal cancer we have recognized two considerations related to incorporating individual heterogeneity that have not been adequately discussed in the literature. First, there are substantial computational gains and interpretation benefits if an individual's life courses are identical except when differences are directly induced by an intervention. Achieving this is not trivial. We have developed the notion of a “common patient” who is the same between scenarios except for intervention-induced changes. We create the common patient using a careful application of Common Random Numbers (CRN). Second, when we model differentiated individuals we can examine differing impacts of polices on specific sub-groups. This leverages the detail in individual attributes to produce useful results for policy makers.