ADULT INDEX OF Bl ELD. 



25 



a divisor. If weight varied exactly with the chest-girth, then the 

 ratio of the former to the latter should remain constant. Such a Btricl 

 relation is hardly to be expected and, of course, is doI found. The 

 ratios obtained show a certain variability aboul the mean condition, 

 and this variability is measured by the standard deviation. Similarly, 

 if each weight be divided in turn by the second and third powi 

 stature, and the corresponding variability of the ratios be considered, 

 we shall have a method of deciding whether weighl varies more 

 closely with the first, second, or third power of chest-girth, and which 

 of those powers gives in its fluctuations the best measure of the cor- 

 responding fluctuations in weight. 



Table 8. — Variability of weight in relation to the second and third 



found in 100 Harvard students. 



A comparison of the standard deviations gives the following results 

 for man : 



weight weight weight 



chest-girth* chest-girth 1 



51.5 77.0 



Ratio: 



chest-girth 

 Standard deviation: 58.3 



