24 THE RELATIVE STRENGTH OF 



local group in this country know that in anthropometric characters it is usually 

 significantly ditU-ri-ntiatrd from any other local f^roup. The population of our 

 suburbs is usually more sedentary than the population in the working class 

 districts of the town itself and less mixed. 



I know, as a matter of fact, that the cephalic index of school children varies 

 very sensibly from one district of London to a second. On this ground alone 

 it is not possible, without control measurements, to assert that, because the 

 percentage of eye defect varies from Whitechapel to Hampstead, the result is 

 due to home environment. It may be so, but a mere statement of percentages 

 in different districts without (a) age distributions, (6) racial proportions, and 

 (c) percentages of defective parents in each district, will not convince those who 

 desire logical statistical proof before forming any conclusion. It is well known 

 that the defective parents also gravitate to the worst districts, and we may 

 expect the defective children there also. For these reasons the work at 

 Edinburgh was especially valuable. It gave age distribution, it dealt with a 

 racially fairly homogeneous material, and it followed up the children into their 

 homes and told us something, if not all we might desire to know, about their 

 parents. I see no other way in which a real solution could be obtained for 

 London. An individual school or two must have all not only the defective 

 children examined, and the eyesight report must be accompanied by a 

 sociological report. 



A report such as that of Dr A. Hugh Thompson on the London school 

 children, in which the numbers at each age of both the normal and the defective 

 children are not given, cannot help the statistician in the least to arrive at 

 definite results. Nor, unless the children are followed into their own homes, 

 is it even possible to say how far bad food, bad air, or parental neglect may 

 account for the presence of any disease. There is always the diathesis as a 

 contributory source, and the fact that all the children in the same family may 

 not be attacked, shows that the variability within the family also plays its part. 



Again my critics will, I hope, pardon me if I say that I am not convinced 

 when I am asked whether this or that "is not a fact." For example, whether 

 it is not a fact that in the better homes the children are more studious, or that 

 the more respectable parents keep their children at home. Either may be the 

 truth, but what we want. are actual numerical measures of the effect of these 

 supposed causes in invalidating the apparently small influence of the environ- 

 mental as compared with the hereditary factor. 



What we want are more data before we conclude that results are paradoxes 

 because of such or such an explanation being "a fact" or "a matter of common 

 experience." 



Let us attempt to get any information we can on the problem of whether 

 the better class parents keep their children at home, and so their offspring are 

 more studious and suffer more from myopia 1 . Now, I know of no statistics 

 which at all touch this point of the studious character of the offspring of better 



1 The reader of our memoir will remember that our conclusion was, not that the 

 better homes produced more myopia, but that there was no marked relationship 

 between bad homes and defective sight. 



