ON THE ETHNOLOGICAL SURVEY OF CANADA. 

 Variability of American Boys. 



445 



I have preferred to calculate in the Toronto series the reduced 

 amounts of variabilities in a different manner. I have grouped the obser- 

 tions according to quarterly periods, and calculated the variabilities for 

 each of these periods. A comparison of the variabilities of these periods 

 and of the full year periods are shown in the following tables : — 



Boys. 



» Six-monthly periods. 



Girls. 



In the following tables I give the averages of our series, with the cor- 

 rections due to the considerations outlined in the preceding remarks. In 

 interpreting these averages it must be understood that the average sizes 

 do not represent the typical values of the measurement, because during 

 childhood the distribution of the measurements is asymmetrical. Owing 

 to the fact that children do not all grow at the same rate, but that some 

 are retarded in development, while others are advanced beyond their age, 

 the rate of growth differs in such a manner that the general distribution 

 of the measurements does not follow the law of probabilities. I will ex- 

 plain this by considering the growth of sixteen-year-old girls. A great 

 many of these girls will have reached the adult stage, and will have ceased 

 growing, while others are not developed according to their age, and con- 

 tinue to grow. If we consider for a moment only those girls who as adults 

 will have a certain stature, we recognise that many will have this stature, 

 while others will still be shorter ; that is to say, the distribution of their 

 statures will be asymmetrical. The same is true of all the other statures, 

 and it will be seen for this reason that the whole distribution will be 

 asymmetrical. On account of this peculiarity of the distribution of sta- 

 tures during the years of growth, the average values of the measurements 

 must not be considered as the types of development for the various ages. 



