I wish to thank Professor Anthony B. Atkinson of the London School of Economics under whose critical eye this study came into being. Without his prompting I would not have chanced upon the topic that is the subject matter of this book, nor would the study have taken this form. His invaluable and expert advice and his constant encouragement over the past four years were crucial to the completion of my work. I should also like to thank Professor Dieter Bös of Bonn University. His detailed comments were an invaluable aid. Finally I must thank Dr Richard N. Vaughan of Cambridge University for many fruitful discussions.