Potential values for the elasticity of substitution then ranged between 0.6 and 1.0 and for the technology share parameter from 0 to 0.4. Without any other constraints on these parameter values, however, the model generates a wide range of forecasts of medical expenditure as a share of GDP. The model is estimated using historical data from 1960 to 20004 and the 10-year forecast (2005 to 2015) from the Centres for Medicare and Medicaid Services. The robustness of the results were evaluated by developing the models from two different measures of income, real per-capita GDP and real per-capita disposable income.