This article is based largely, but not entirely, on a thesis which was completed at Columbia University in 1952. The thesis could not have been written without the cooperation of the various rating organizations. They generously supplied the author with copies of their plans and they answered promptly and clearly his oral and written requests for clarifying information. Special mention should be made of Mr. Edward S. Allen, Actuary, Compensation Insurance Rating Board of New York, who read the entire thesis and suggested some important changes. The author also wishes to thank Professor Richard Heins of the University of California who read the first draft of this article and who made many constructive comments which improved the contents and its presentation immeasurably.
The topic was originally suggested by Professor Robert Riegel of the University of Buffalo who also read the entire thesis in its early stages and made many constructive criticisms. The many important improvements that were made in form and content before the thesis was completed were due largely to careful editing by Professors Ralph H. Blanchard and Oscar N. Serbein of Columbia University. The author is deeply indebted to all of these people for their help.