The First Edition of this book was published in 1937 with George W. Snedecor as the sole author. Snedecor asked William G. Cochran to do the revisions for the sixth edition, and Cochran was listed as the second author of the sixth and seventh editions. The present edition was prepared by several members of the Department of Statistics at Iowa State University. The revisions were guided by the principle that the work should remain the work of its original authors; thus, much of the material remains as previously published. A significant change in this edition occurs in the notation used to describe the operations of multiple regression. Matrix algebra replaces the original summation operators, and a short appendix on matrix algebra is included.