Modeling inter-regional patient mobility : does distance go far enough?

Gravity models are extremely popular to investigate economic interactions across space. Bilateral ows are usually available as regionally aggregated data only, while information on demand and supply is often available at a finer spatial scale. We suggest using this information to calculate a measure of spatial accessibility based on the two-step oating catchment area method to augment the gravity equation. We apply this idea to analyze patient mobility by using easily available and spatially explicit information on physicians' locations (supply) and grid-level population data (demand). Our approach improves the model's fit and allows conducting a rich set of simulation experiments.