This study is a revised version of my Ph.D. thesis submitted to the Department of Economics at the Massachusetts Institute of Technology in 1968. I owe a great deal of gratitude to Professors Franklin M. Fisher, Edwin Kuh, and Robert M. Solow for their many helpful comments and suggestions throughout the course of this work. I would also like to express my appreciation to William D. Nordhaus for help at various points in this study. Most of the computer work was done on the IBM 7094 computers at MIT and Princeton University. The research for this work was partly sponsored by the National Science Foundation and the Woodrow Wilson National Fellowship Foundation, to whom I am grateful. The revision was sponsored by a grant from the Oﬀice of Manpower Policy, Evaluation, and Research of the US Department of Labor.