PREFACE TO THE SECOND EDITION. 



THE first edition of this book having been favorably re- 

 ceived, the publishers have authorized a revised edition 

 embodying many of the new statistical methods elaborated 

 chiefly by Professor Karl Pearson and his students and 

 associates, and presenting a summary of the results gained 

 by these methods. These, while increasing somewhat the 

 bulk of the book, have, it is hoped, rendered it more service- 

 able to investigators. Too much emphasis can hardly be 

 laid on the debt that Biometricians owe to Professor Pear- 

 son's indefatigable researches in the new science of Biome- 

 try especially in the development of Statistical Theory. 



The publishers, also, of this book are deserving of credit 

 for the courage they have shown in reproducing expensive 

 tables for the use of a still very limited body of statistical 

 workers. Especial attention is called to Table IV, which 

 is an extension of Table IV of the first edition that was cal- 

 culated by Professor Frederick H. Safford, and appears to 

 have been the first published table of the normal probability 

 integrals based on the standard deviation. More recently 

 Mr. W. F. Sheppard has published in Biometrika a similar 

 table in which, however, the tabular entries are given to 

 seven places of decimals, while the arguments are given 

 to two decimal places only. In the present table the argu- 

 ments are subdivided to three places of decimals and with 

 the aid of the table of proportional parts interpolation is 

 easily effected. 



Especial acknowledgment must be made of assistance 

 received from my friend Mr. F. E. Lutz, who read over the 

 entire manuscript and contributed certain of the numerical 

 examples. 



STATION FOR EXPERIMENTAL, EVOLUTION 



OP THE CARNEGIE INSTITUTION, 



COLD SPRING HARBOR, 



March 27, 1904. 



iv 



