The GRIEG model is a hybrid model of demo-economic projections that combines two approaches: the econometric approach - based on the micro-economy - of the New Economic Geography (NEG) and the stochastic approach of the topodynamic model. The data required by the NEG part of the model being only available for the United States, the hybrid version could be applied only for the United States. In contrast, the version excluding the NEG component was applied to the entire world (including USA) since the topodynamic part of the model requires data available for all countries. This paper makes a comparative analysis of the population, production and product per capita projections for the United States using the two versions of GRIEG (the version without NEG component and the hybrid version). The results of this comparison tend to confirm the validity of the purely topodynamic version where the hybrid version is not applicable, and the interest of the hybrid model where data exist.