A. M. Carr Saunders 
361 
TABLE V. 
Percentages of Boys and Girls who have had the following Diseases. 
Age 13. 
Measles, Boys 75 - 2 Whooping Cough, Boys 37"1 Scarlet Fever, Boys 16"3 
„ Girls 85-4 „ „ Girls 44-9 „ „ Girls 18'4 
Diphtheria, Boys 39 Mumps, Boys 2D4 Chicken Pox, Boys 28'6 
„ Girls 4-7 „ Girls 23-2 „ „ Girls 35-5 
This gives the percentages of boys and girls who have had the various diseases. 
It will be seen that not only do the older girls have, as before shown, a higher 
average number of diseases, but in each case a higher percentage of girls have had 
the disease than of boys ; and further, the differences between the percentages as 
a fraction of the whole are roughly the same between boys and girls. The differ- 
ence is rather greater in the case of diphtheria and rather less in the case of 
mumps ; but on the whole there seems to be a consistently higher average among 
the girls for each disease. If we now turn back to the incidence and mortality 
rates, it is evident that they show the first explanation suggested to be impossible. 
The incidence rates are not the same for both sexes, and the mortality rates do 
not show that marked and persistent mortality among the younger hoys which 
the explanation supposes. In the case of whooping cough there is a far higher 
death rate among girls, and here the explanation breaks down entirely ; for as 
Table V shows, the difference between the two sexes is as marked as in any 
other disease. It must, of course, be remembered that we are here only dealing 
with six specified diseases ; the elimination of boys, which we know to occur, 
must take place through the agency of other diseases. 
The figures for the incidence rate suggest a further explanation. Un- 
fortunately they are only obtainable for scarlet fever and diphtheria. But in 
these two cases the girls from 5 years of age and upwards are more liable to 
attack. Now, if the death rate were the same for both boys and girls, then this 
would be an explanation, in so far as the bare fact that girls are as a matter of 
fact more susceptible to disease than boys is an explanation. If we examine the 
death rates for diphtheria and scarlet fever, we see that they are not the same; the 
general tendency is for the rate among the younger boys to be higher than that 
among the younger girls, and the opposite way about for the older children. On 
the whole, however, up to the age of 15 diphtheria is a more fatal disease for girls 
than boys, while the case is reversed in scarlet fever. In such cases as that of 
diphtheria, in which the death rate is higher among girls, there must be a tendency 
to counteract the results of the higher incidence rate among girls, and in the girls 
of 13, as shown in Table V, we might expect to find such a large difference between 
the sexes as in the other cases. But, as already pointed out, the difference between 
the two sexes in the case of diphtheria is rather larger than for other diseases. 
The explanation is, it must be admitted, not very satisfactory ; but granted the 
existence of the higher incidence rate among girls, we must suppose that the 
Biometrika vm 46 
