A. M. Carr Saunders 
359 
When we turn to consider the average number of diseases per head in the two 
sexes, we do find a significant difference, but only in the children of the older group. 
Boys from 3 — 7 and girls of the same age have almost exactly the same number 
of diseases per head. The difference only occurs between the boys and girls aged 
13, and betvveeu them it is marked, the boys having an average of l - 83 and the 
girls one of 212 diseases per child. 
Now, the source of this fact is by no means clear ; there are two possible 
explanations which may be at once put aside as not applicable here. In the first 
place the difference cannot be due to bias. For if there were any reason why the 
diseases of the girls should be remembered more vividly than those of the boys, 
then that reason ought to work in the case of the younger children as well. But 
it does not seem possible to find any such reason. Dr Auden has, indeed, pointed 
out to me that a parent is more often present during the examination of girls 
than of boys. Taking about 1500 of each sex, he calculated that a parent was 
present when 65 per cent, of the boys and 71 per cent, of the girls were being 
examined. But I agree with him in thinking that this could not possibly account 
for the difference in the average number of diseases per child in the two sexes. 
In the second place it is not due to an epidemic among the girls, since the girls 
are found to have had a higher average number of all the six diseases with which 
we are dealing. 
The first explanation of this anomaly which promised to be at all sufficient is 
connected with the fact that, although more boys are born than girls, yet in a few 
years the numbers of the two sexes become equal, and later the girls outnumber 
the boys. So far these facts are a matter of common knowledge, and the manner 
in which it was at first thought that they might explain the above figures was as 
follows. If we suppose that the incidence rate for the special diseases with which 
we are concerned is of equal intensity for the two sexes, and that more boys die 
from these diseases than girls, then if a number of boys and girls aged 13 were 
examined, we might expect to find more girls who had diseases than boys ; for 
supposing an equal number to have been attacked from each sex, and a greater 
percentage of boys to have died, there will clearly be present at a later age more 
girls living who have had diseases. Now, this explanation does not as a fact hold 
good, as will appear ; but it was while examining data bearing on these points 
that certain facts were found which do help to elucidate the question. 
The above reasoning rests on the assumptions that (!) the incidence rate is 
equal or at least not very dissimilar in the two cases, and (2) the death rate is 
higher among boys than girls. Firstly as to the incidence rate : — the age distri- 
butions of the cases of scarlet fever and diphtheria notified to the Metropolitan 
Asylums Board as given in the Board Report for 1900 were extracted. These 
figures alone do not give an accurate measure of the incidence, since an allow- 
ance must be made for the fact that the numbers of the two sexes are not equal 
at the different ages. The total numbers of the two sexes for the various age 
