YITAL STATISTICS. 
J 471 
and as a measure of that condition when com¬ 
pared with another nation, or with the same 
nation at another time, in ignorance or for¬ 
getfulness of the well-ascertained fact that the 
living population of one nation may differ 
very widely in its composition from the living 
population of another, and that the elements 
of the population of the same nation may 
undergo very extensive changes even in a 
short term of years. 
In illustration of the first of these state¬ 
ments, it will suffice to instance the strongly- 
contrasted populations of England and Ame¬ 
rica, of which the first has 46 and the second 
54 in the hundred under 20 years of age, the 
number above 20 being, of course, reversed. 
In the two populations of Denmark and Sar¬ 
dinia, on the other hand, the relative pro¬ 
portions at different ages are very nearly the 
same ; and, when expressed in round numbers, 
for long intervals of age, identical. As a 
general rule, however, there is considerable 
difference between one population and another 
in the proportion of persons living at the 
same ages. In support of the second of these 
statements, the change which took place in 
the population of England in the interval 
from 1821 to 1841 may be adduced. At the 
former period, the persons living under 20 
years of age were 49 per cent, of the whole 
population, but in 1841 they had fallen to 46 
per cent. 
There is no room for doubt, therefore, that 
different populations vary in their composition, 
and that the same population may, in course 
of time, undergo considerable changes, and 
exhibit very striking contrasts in the number 
of persons living at different ages. 
Such being the case, it will not be difficult 
to prove that the differences in question do so 
materially affect the mean age at death as to 
rob it of its alleged value as a test or measure 
of the sanitary condition of nations. We 
have only to suppose the young population of 
America transferred to England, and exposed 
to the same causes of death as determine the 
duration of life of its own inhabitants, in 
order to be fully convinced of the fallacious¬ 
ness of this test. Now, according to the 
rate of mortality prevailing in England, little 
more than half its inhabitants die before com¬ 
pleting their 20th year, and somewhat less 
than half after that age. If the mean age of all 
who die under 20 years of age be taken at 5 
years, and of all who die above 20 at 60 years, 
the mean age at death of fifty persons dying 
out of the respective populations of England 
and America, will be about 34 and 30 years. 
These numbers, however, though correctly 
calculated from the rough data just assumed, 
diverge much less widely than the true re¬ 
sults, for the actual mean age at death, which 
is 29 years in England, is only 20 years in 
America.* * So that two populations, subject 
to the same law of mortality, and losing the 
same number of persons at the same ages, in 
* See an essay by F. G. P. Neison, Esq. in the 7th 
volume of the Journal of the Statistical Society. 
consequence of the different constitution of 
their respective populations, may have a 
widely different mean age at death. Similar 
results to those obtained by comparing Eng¬ 
land and America are arrived at if we compare 
England in 1821 with England in 1841. The 
mean age at death, which in 1821 was 25 
years, became in 1841, owing to the change in 
the population already referred to, 29 years.* 
If any further illustration of the fallacy of the 
mean age at death, when used as a test of the 
sanitary state of nations, were required, it might 
be found in its failure when applied to coun¬ 
tries of which the true position in the sanitary 
scale has been ascertained by the application 
of unexceptionable tests. The three nations, 
England, France, and Sweden, for example, 
occupy the following relative position :— 
1. England. 2. France. 3. Sweden. 
But if the mean age at death were taken as 
our guide, they vrould rank as follows :— 
1. France. 2. Sweden. 3. England. 
The mean age at death being 34 for France, 
31 for Sweden, and only 29 for England, t 
b. The mean age at death has been em¬ 
ployed as a measure of the relative sanitary 
condition of English counties, cities, and 
towns, of town and country, and of the several 
districts of large cities. To show the fallacy 
of the method as so applied, it will suffice to 
prove that the populations thus compared are 
composed of different elements. Taking, as 
before, the number living below 20 years of 
age as an illustration, it appears that while 
there are 47 in the hundred under 20 in 
Essex and Suffolk, there are only 44 in the 
hundred under 20 in Staffordshire ; that for 
47 in the hundred in Leeds, 46 in Sheffield 
and Birmingham, and 44 in Manchester, 
there are only 42 in Liverpool, 41 in Exeter, 
and 40 in London ; and, lastly, that the popu¬ 
lation under 20 years of age, which amounts 
to 47 per cent, in Bethnal Green falls as low 
as 41 in Clerkenwell, 40 in Kensington, 36 in 
St. Gdes’s and Marylebone, and 31 in St. 
George’s, Hanover Square. The effect of 
this variable distribution of the population on 
the mean age at death is very well marked, 
and is placed in a very striking light by sup¬ 
posing the population of the metropolis to be 
transferred to some of these counties and 
cities, and to be exposed to the influences for 
good or evil which are brought to bear on the 
duration of life of their actual populations. 
Thus, if the population of London, of which 
40 per cent, are under 20 years of age, were 
to be transferred to the county of Hereford, 
The exact age, deduced from the rough data as¬ 
sumed in the text, will be as follows : — 
England, ~ x 5 +S*x60=115+1620=1735, which, di¬ 
vided by 50, gives 347 as the average age. 
America, ^x5 +^X60 =135+1380=1515, 
which, 
di¬ 
vided by 50, gives 30‘3 as the average age. 
* For the facts on which these comparisons are 
founded, see an essay in the 6th vol. of the Journal 
of the Statistical Society. By G. R. Porter, Esq. 
t See the 6th annual Report of the Registrar 
General, p. 572.