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Based on a Constant Elasticity Substitution (CES) system, Anderson and van Wincoop (2003) used a Non-linear Least Squares (NLS) model considering the endogeneity of trade costs to refine the theoretical foundations of the gravity model and provide evidence of border effects in trade.

Based on a Constant Elasticity Substitution (CES) system, Anderson and van Wincoop (2003) used a Non-linear Least Squares (NLS) model considering the endogeneity of trade costs to refine the theoretical foundations of the gravity model and provide evidence of border effects in trade.