VITAL STATISTICS. 



classes of society, and of the members of 

 different professions, without reference to 

 their place of residence. But little objection 

 can be made to this test when applied with 

 ordinary precaution. If the earliest age ad- 

 mitted into the tabular abstracts, from which 

 the averages are calculated, is the same in all 

 the classes submitted to comparison ; if during 

 the time over which the observations extend 

 the classes compared with each other have 

 received no rapid accession of numbers ; and 

 if the deaths are those of the whole body of 

 the profession or trade (or, if of a section 

 only, then of a similar section in every case), 

 the mean age at death will constitute a fair 

 measure of the relative sanitary condition of 

 the several classes in question. But if, on 

 the other hand, two professions or occupations 

 are compared, in which the age at entry is not 

 the same ; or the one is stationary in point of 

 numbers, while the other is rapidly increasing ; 

 or if the whole body is taken in the one case, 

 and only the senior or junior members in 

 the other, the results will be quite unworthy 

 of confidence. 



Some of the greatest misapprehensions 

 existing with respect to the duration of life of 

 certain classes of the community, are traceable 

 to the selection of the senior members of a 

 class to represent the entire class to which 

 they belong. Nothing is more common, for 

 instance, than to hear royal families, or the 

 members of the aristocracy, or the clergy, or 

 the army, spoken of as long-lived, on the 

 strength of the advanced ages attained by 

 kings, peers, archbishops, or general officers. 

 In making a selection of the more conspicuous 

 members of the class, the significant fact is 

 overlooked that they are also the oldest 

 members, and that they do not attain their 

 exalted rank till a period of life greatly in 

 advance of that at which they entered their 

 several professions. The mean age, at death, 

 for example, of archbishops and bishops of 

 the established church, is upwards of 71 

 years, but the mean age at death of the whole 

 body of the clergy is about 64 years. A 

 similar disparity would be found to exist be- 

 tween the peers and the whole body of the 

 aristocracy, and between general officers in 

 the army, and admirals in the navy, and the 

 whole body of officers in the two branches of 

 the public service. 



The tables already referred to as comparing 

 the four classes of gentry, tradesmen, artisans, 

 and paupers in the several districts of the 

 metropolis, supply analogous examples of 

 erroneous selection and classification. In the 

 great majority of the metropolitan parishes, for 

 instance, there is no class of gentry properly 

 so called ; but this class consists, with the 

 exception of a few professional men not im- 

 properly mixed up with it, of tradesmen who 

 have retired from business long enough to be 

 entered in the mortuary registers as gentle- 

 men. On the other hand, the pauper class 

 is very largely recruited from the ranks of 

 the artisans and labourers, and contains a 

 very considerable proportion of old persons 



who, being no longer able to earn their liveli- 

 hood, have come upon the public for .support. 



The mean age of the living has been occa- 

 sionally resorted to as a test or measure of 

 salubrity. It has been assumed that a low 

 average age of the living members of a class, 

 when compared with the average age of ano- 

 ther class, arises, cceteris paribus, from a high 

 mortality leading to a quick addition of young 

 members. This assumption is justified only 

 in those cases in which the addition of young 

 members can be shown not to arise from any 

 other cause, such as an increased demand for 

 members of the class in question. It is there- 

 fore a test to be employed with great caution; 

 and it will also be necessary to show that the 

 age of admission of the classes subject to com- 

 parison is the same, or open only to very 

 slight variation. 



2. The rate of mortality. The mortality, or 

 rate of mortality, is the number of deaths 

 which takes place in a given population, in a 

 given space of time. The calculation is gene- 

 rally made for a year, so that the ratio comes 

 to express the number of the living out of 

 which one will die annually. The ratio is 

 sometimes stated as a fraction, and sometimes 

 as a percentage proportion. If, for in- 

 stance, out of a living population of 100,000, 

 two thousand deaths take place every year, 



T<?<5,info or T&> . r 2 P er ce . nt - is the mortality, 

 or rate of mortality, to which that population 

 is exposed. 



In estimating the value of this test, it is 

 necessary to bear in mind that the rate of 

 mortality varies for every year of life. It 

 follows, therefore, as a natural consequence, 

 that the rate of mortality, like the mean age 

 at death, must be materially influenced by 

 the ages of the living population. lr\ a po- 

 pulation containing a large proportion of 

 young children, subject to a very high mor- 

 tality, the aggregate rate of mortality for the 

 entire population will be necessarily higher 

 than in a population abounding in older per- 

 sons and having a comparatively small number 

 of children. But a very cursory examination 

 of tables of mortality will convince us that 

 the error attaching to the rate of mortality 

 as a test or measure of the sanitary condition 

 of a population is much less than that which 

 is inherent in the mean age at death ; for not 

 only do the extremes of life approximate much 

 more closely to each other in their respective 

 rates of mortality than in the mean ages at 

 death, but ages which, though less widely 

 separated, are far enough apart to affect the 

 mean age at death, are exhibited as subject 

 to a mortality very nearly identical. From 

 5 to 10 years of age, for example, the rate of 

 mortality, in the male population of England, 

 is '970 per cent., and from 20 to 30 years 

 of age '974- per cent. ; so that, while out of 

 100,000 persons dying at the respective ages of 

 5 10 and 20 30, 970 and 974 personswould 

 die in the year, their age at death would count 

 in the one case as something between 5 and 

 10, and in the other at some age between 2 j 

 and 30. The difference in the rate of rnor- 



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