mj ITS VARIABILITY 81 



I have taken Boas's determinations of variability (cr) {op. cit. 

 p. 1548), converted them into the corresponding coefficients of 

 variability {a[M x 100), and then smoothed the resulting numbers. 



Coefficients of Variability in Annual Increment of Stature. 



Age 7 8 9 10 11 12 13 14 15 § 



Boys 17-3 15-8 18-6 191 21-0 24-7 29-0 36-2 46-1 

 Girls 17-1 17-8 19-2 22-7 25-9 29-3 37-0 44-8 — 



The greater variability of annual increment in the girls, as 

 compared with the boys, is very marked, and is easily explained 

 by the more rapid rate at which the girls run through the several 

 phases of the phenomenon. 



Just as there is a marked difference in "phase" between the growth- 

 curves of the two'sexes, that is to say a difference in the periods when growth 

 is rapid or the reverse, so also, within each sex, will there be room for similar, 

 but individual phase-differences. Thus we may have children of accelerated 

 development, who at a given epoch after birth are both rapidly growing and 

 already "big for their age"; and others of retarded development who are 

 comparatively small and have not reached the period of acceleration which, 

 in greater or less degree, will come to them in turn. In other words, there 

 must under such circumstances be a strong positive "coefficient of correlation" 

 between stature and rate of growth, and also between the rate of growth in 

 one year and the next. But it does not by any means follow that a child who 

 is precociously big will continue to grow rapidly, and become a man or woman 

 of exceptional stature. On the contrary, when in the case of the precocious 

 or "accelerated" children growth has begun to slow down, the backward 

 ones may still be growing rapidly, and so making up (more or less completely) 

 to the others. In other words, the period of high positive correlation between 

 stature and increment will tend to be followed by one of negative correlation. 

 This interesting and important point, due to Boas and Wissler*, is confirmed 

 by the following table : — 



Correlation of Stature and Increment in Boys and Girls. 

 {From Boas and Wissler.) 



I.e. p. 42, and other papers there quoted. 



