9Bergstrand,J.H., (1989) "The Generalized Gravity Equation, Monopolistic Competition and the Factor Proportions Theory in International Trade," The Review of Economics Statistics 71, 143-153
10Brada,J.C. and J.A.Mendez, (1985)“Economic Integration among Developed, Developing and Centrally Planned Economics: A Comparative Analysis,”The Review of Economics and statistics 67, 549-556