26 LABORATORY MANUAL OF ANTHROPOMETRY 



and pencil as well, while the paper is held vertically, like an artist's 

 canvas. 



SIMPLE BIOMETRIC METHODS 



I. Indices 



The Index of a given measurement is its percentage when compared 

 with some other measurement taken as a standard, or the equivalent of 

 100. It is thus a relative, and not an absolute, term, and may be com- 

 pared directly with the corresponding index in another individual of 

 different size. 



For example, imagine three heads as seen from directly above; in 

 one, which is long and narrow, the breadth is exactly one-half the length; 

 in another the breadth is three-fourths the length; and in the third, which 

 is absolutely circular in this outline the breadth and the length are equal. 

 Now, if the total length were exactly the same in all, for instance, 160 mm., 

 the three breadths would be respectively 80, 120, and 160, and they 

 could be directly compared; if, however, they were not alike, we could 

 say that in the first the breadth was 50% of the length; the second, 75%, 

 and the third 100%, and these proportions could be compared directly, 

 although the actual measurements in millimeters could not. 



These are the indices, i.e., the proportions of the breadths to the 

 lengths. Whatever the actual lengths, they are considered to equal 100 

 in all cases, and the breadths are expressed as so many parts of that 100. 

 The question is, if the length equals 100, what does the breadth equal?; 

 or length : breadth :: 100 : x. This is solved by converting this expres- 

 sion into the following: 



breadth X 100 



length 



which will give the value of the breadth, in terms of the length, or, in 

 other words, the index. 



Illustration. The total length of a given skull is 190 mm., and its 

 breadth is 141 mm. We now divide the number, the percentage of 

 which is to be found by the one which is to stand for 100, first adding 

 two ciphers to the dividend, thus: 



190)14100(74.21 index 

 1330 

 800 

 760 



400 

 380 



200 



190 



The breadth, 141, is thus about 74% of the length, and this index is to 

 be compared directly with the like index of any other skull, whatever its 

 size. 



Skulls of as large an index as 100 or as small a one as 50, mentioned in 



