VITAL STATISTICS. 



1471 



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 1S21 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 18 il 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 E.G. P. Xeison, 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 iige 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 would 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. Giles'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 + ;/ *x60=115+ 1620=1735, which, di- 

 vided by 50, gives 31'7 as the average age. 



America, 5ix 5+^x60 =135+1380=1515, which, di. 



vided by 50, give* 30 3 as the average age. 



* For the facts on which these comparisons are 

 founded, see an essay in the Cth vol. of the Journal 

 of the Statistical Society. By G. R. Porter, Esq. 



i See the Gth annual Report of the Registrar 

 General, p. 572 



