INFLUENCE OF ORDER OF BIRTH, ETC. 303 
than among the affected persons themselves. This would be the 
case if the affected families were small. It is very desirable to 
have data on the relative position of the affected person in indi- 
vidual families of two, three, four, five, etc., persons so that it 
could be ascertained whether or not within the limits of families 
of a given size the marked individuals occur in preponderating 
numbers in any given position. Data grouped in this way would 
enable us to avoid several pitfalls incident upon handling mass 
statistics. In the data of Weeks on the order of birth of epileptics 
there is, as Pearson states, ‘‘no excess of the eldest-born in the 
individual families; if there be any excess it is in the interme- 
diates. Thus, if we may trust this data, which are slender, there 
is no weighting of the first-born in the case of epilepsy unless it 
arises from the weighting of small families.” Treating the data 
by the methods employed in other cases Pearson finds an excess 
of epileptics among the first born. ‘‘We must, I think, conclude,” 
he remarks, “‘by recognizing that, while there is a weighting in 
epilepsy, this is due to a selection of families rather than to a 
selection of the elder-born in each family.”’ How far the rela- 
tively large proportion of first-borns in Pearson’s data on other 
defects may be due to the selection of small families is, of course, 
uncertain. It is of value to know, however, whether the relative 
preponderance of the first born in pathological stocks is due to the 
smallness of the family. As Pearson remarks, ‘‘We are shooting, 
so to speak, at the entire population of first borns, and a bias with 
regard to selection of weaker families may come in, in much the 
same way as families up to six or seven may be the sign of healthy 
parents, and so the offspring will be less liable to disease. This 
idea cannot be excluded. But in itself it indicates how inadequate 
is the proposal to treat the problem only within families of con- 
stant size.” 
However it happens that the first born in the population in 
general comes to be selected for defect or disease, the reduction 
of the size of families leading to an increase in the relative propor- 
tion of first born individuals will inevitably cause an exaggeration 
of several undesirable hereditary traits. In so far as the birth 
