INFLUENCE OP THE AGE OF THE PARENTS 25 



It will be seen that the excess of male births in the general average 

 markedly exceeds its normal value. We must regard this divergence as 

 unreal and attribute it to the greater liability of a female child to be 

 omitted from the record. As this omission would be probably about 

 equal in the case of all the successive children, we may assume that the 

 values of E m are all eqiially in error from this cause. The normal value 

 from the statistics of birth being about 2.4, while the count gives 4.6, 

 we subtract the excess, 2.2, from each separate value of E m and thus 

 obtain corrected values of the percentage of excess, which are found in 

 the last column. 



It will be seen from the numbers of this column that the excess of 

 males among first-born children exceeds G per cent. This shows that 

 there are about eight males to seven females of this class. But, in the 

 case of the second child, the percentage of excess drops to 2.2, which is 

 slightly blow the normal and, in the case of the third child, it becomes 

 negative, showing that, after we correct the supposed defect of the 

 record, there is actually a slight excess of female births. 



The rapidity of the drop from 6.7 in the case of the first birth to 2.2 

 in the case of the second and then to a negative quantity in the case of 

 the third, seems to show quite conclusively that the excess of males in 

 the number of the first-born children is not attributable to the age of the 

 mother, but to the fact that it is a first child, irrespective of age. That 

 the fall is too rapid to be the effect of age is shown in the following way : 

 The difference of age at the birth of the first and third child is not 

 likely to have been more, in the general average, than three years. Xow 

 a drop of 4 in the percentage in three years would imply a drop of 

 twice this amount between the ages of 17 and 24, which we may take 

 as the probable range in the case of a first child. The approach to 

 uniformity in the percentage in these cases where the marriage must have 

 been at such different ages, precludes the supposition that age is the main 

 factor in the case. 



Continuing our study of the table, we find a remarkable uniformity 

 in the number of male and female births up to the eighth child. In 

 the case of the second child the excess is still fairly well marked. Thus 

 we may conclude that the tendency toward male excess, though 

 greatly diminished, is probably not wholly obliterated in the case of 

 the second child. But from the fourth to the eighth inclusive, the devia- 

 tions are so small that we may regard them as the effects of accident. In 

 the case of the six children from the third to the eighth, it would seem 

 that the birth of the two sexes is equally probable. Then, from the 



