Acknowledgements

Thanks are due to many people for many helpful discussions. They include our colleagues Greg Bennett and Winston Cherry of the Department of Statistics and Actuarial Science, astronomers Judith Irvin of Queen's University and Dieter Brookner of Kingston who pointed out Cotter's book [14] to us, and Stephen Stigler of the University of Chicago for his helpful comments on early drafts of this paper.

All quantitative graphics were produced using the Quail statistical software environment now available on the world-wide web.