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.