Palin Elderton and Ethel M. Elderton, Adam and Charles Black, London; "Statistical Averages," by Franz Zizek, Henry Holt and Company, New York; "Statistical Methods with Special Reference to Biological Variation," by C. B. Davenport, John Wiley and Sons, New York. Any list of this sort is, of course, incomplete and these books are mentioned as only a few of those which may be found useful to supplement the study of the subject considered in this volume.

Part of the matter here presented was given in lectures delivered at the Graduate School of Business Administration of Harvard University, the Amos Tuck School of Administration and Finance of Dartmouth College, the Northwestern University School of Commerce, and the College of Commerce and Administration of the University of Chicago. Some of the material was presented before the American Society of Mechanical Engineers in New York. The advance presentation of matter in course of preparation for the press was made with the cordial assent and approval of the publishers of this work.

I am greatly indebted to Mr. Edward Scott Swazey, Mr. Curtis Prout, and Miss Katherine Tyng, for valuable assistance and suggestions received during the preparation of this book. Chapter XV is largely based on an article prepared at the

PREFACE Vll

suggestion of the author by Mr. Pierpont V. Davis of New York City and pubUshed by Mr. Davis in Moody's Magazine. I wish also to express my thanks to numerous friends who have given excellent suggestions and criticisms during the time the manuscript was in preparation.