SOME ASPECTS OF THE BIOLOGY OF HUMAN POPULATIONS 54 1 



performance of more or less routine tasks, in contrast to 

 the persons composing the reconstituted class 7, who, in the 

 large, get their Hving rather more by the exercise of their 

 wits than of their muscles. 



In order that there may be no misunderstanding the 

 names of the main occupational classes which have been 

 altered by the described procedure will be printed in italic 

 type throughout. This typographical usage will serve to 

 indicate that the statistics so printed are for the reconstituted 

 classes, and not for the classes originally so named in the 

 official report. 



The next and final point of method to be considered 

 before coming to the results is that of age. The ideal in 

 all studies of fertihty is, of course, the completed family. 

 In the present case this ideal cannot be precisely attained 

 from the available data. General consideration of the 

 problem, and careful examination of all the figures them- 

 selves as given in the original report, led finally to the 

 decision to deal analytically with the data for fathers aged 

 forty-five and over. This procedure will probably give as 

 close an approximation as it is possible to get, from these 

 or similar records extracted from the official standard 

 birth certificate of the United States, to the unknown 

 average size of completed family for the different occupational 

 classes. 



Table vi represents the first set of basic data which we 

 shall need in the discussion. 



Before discussing at all the results of this table, it is 

 necessary to consider some of the important peculiarities 

 of the data. In the first place, if the figures of column d 

 could be regarded as representing exclusively completed 

 famihes, which they almost but not quite can, they would 

 still give an erroneous impression of the gross fertility of the 

 several occupational classes, for the following simple reason. 

 All the data in the table are derived from the experience of 

 women who were mothers in 1923. That is to say, they 

 were women who were fertile in that particular year. No 

 other women are included. No sterile matings appear, 

 and no matings of generally low fertility throughout the 

 mated Hfe, except the few in which the female chanced to 



