268 



MEMORIES OF MY LIFE 



cision to the meaning of "class-place." The familiar 

 phrases of top of his class, near the top, half-way down 

 it, and the like, express a great deal, but they express 

 much more if used in connection with the size of the 

 class. A useful way of reducing classes of all sizes 

 to a common one is as follows. The names of the 

 individuals are entered in the order of their class- 

 places in a long column, beginning with the highest. 

 The names are separated by lines which resemble the 

 rungs of a ladder, and will here be called rungs for 

 distinction. The interval between the lowest and 

 highest rungs is divided along the sides of the ladder 

 into equal parts to form a scale, usually one of 100 

 parts. In this the lowest rung stands at o and the 

 highest at 100. Such divisions are called centiles. 

 If the divisions are not in hundredths, but otherwise 

 as tenths, eighths, or quarters, they are still called by 

 words ending in " ile," as decile, octile, and quartile. 

 The marks corresponding to the class-places at each 

 centile, decile, octile, or quartile, are independent of 

 the size of the class, except in that small degree to 

 which all statistical deductions are liable when derived 

 from different samples of the same store of material. 



The diagram opposite explains the process. For 

 reasons of space it is adapted here to a class of only 

 twelve individuals, but it is applicable equally well to 

 classes however large, and the larger the better. 



The method of centiles affords a convenient and 

 compact way of comparing the amounts of specified 

 faculties in different individals. All this is an 

 old tale now, but I had to take a great deal of 

 trouble before it was clearly thought out and well 

 tested. 



