1474 



VITAL STATISTICS. 



tality would be almost nothing, while the dif- 

 ference in the age would amount to about 

 20 years. So also if we compare individual 

 years instead of terms of years. The mor- 

 tality at 10 years is -791 per cent., at 20 years 

 784 per cent. ; at 1 1 years it is '702 per cent., 

 at 18 years .709 per cent. The rate of mor- 

 tality differs very slightly in the ages brought 

 under comparison, while the mean age at 

 death differs by 10 and 7 years respectively. 



These a priori reasonings are fully borne 

 out by the results of actual comparison. In 

 one of the reports of the Registrar General * 

 the expectation of life (which will be presently 

 shown to be the true test or measure of the 

 sanitary state of a population), the mortality, 

 and the mean age at death, for six different 

 populations, are compared with each other, 

 with what result the following table will show. 



Expectation of life, in years : Surrey, 45 ; 

 England, 41; France, 40; Sweden, 39; Metro- 

 polis, 37 ; Liverpool, 26. 



Rate of mortality, or one death in Surrey, 

 52; England, 41; France, 42; Sweden, 41; 

 Metropolis, 39 ; Liverpool, 30. 



Mean age at death, in years : Surrey, 34 ; 

 France, 34; Sweden, 31 ; England, 29;" Me- 

 tropolis, 29; Liverpool, 21. 



The rate of mortality, then, keeps pace 

 with the expectation of life, to such an extent, 

 at least, as to place the six communities in 

 the same relative position ; while, according 

 to the mean age at death, the nations which 

 stand third, fourth, and fifth on the list suffer 

 transposition, France and Sweden taking 

 rank before England in the scale of salubrity, 

 and England, which holds, of right, the second 

 place immediately after her own county of 

 Surrey, is made to descend to the fourth rank. 

 When compared, therefore, with an accurate 

 measure of the duration of human life, the 

 rate of mortality shows itself more worthy of 

 confidence than the mean age at death. 

 Nevertheless, for reasons already assigned, it 

 must not be looked upon as altogether free 

 from objection, and must, in every case, be 

 regarded as of inferior value to the test next 

 to be considered, namel}', 



3. The expectation of Ife. The expectation 

 of life, or the mean future life-time, is the 

 mean number of years which, at any given 

 age, the members of a community, taken one 

 with another, may expect to live. This ex- 

 pectation is embodied in those series of cal- 

 culations which are technically known as life- 

 tables, and which are so largely in use in the 

 important operations of life-assurance. When 

 correctly calculated, they are based on the 

 two concurrent series of facts, the numbers 

 and ages of the living and the numbers and 

 ages of the dying, and they therefore comprise 

 the two elements necessary to perfect ac- 

 curacy. When based upon the ages of the 

 dying alone, they are open to nearly the same 

 objection as those which apply to the mean 

 age at death. 



The following is an abbreviation of the 

 English life-table, which will bo found given 

 * Sixth Annual Report, p. 572. 



at length for any year of life from birth to 95 

 years of age in the fifth annual report of the 

 Registrar General.* 



The table is read thus : At birth the ex- 

 pectation of a male child is 40'19 years, of a 

 female child 42-18 years ; at 5 years of age 

 the expectation is 49 64 years for a boy and 

 50-38 years for a girl ; at 20 years of age, 

 males one with another may expect to live 

 39'88 years, and females 40'81 years ; at 30 

 the expectation has fallen to 33' 13 for men 

 and 34-25 for women. 



4. The mean duration of life, the mean life, 

 the mean life-time, or vie moyenne, is found 

 by adding the age to the expectation of life. 

 Thus the mean duration of life at 5 years of 

 age is 5 + 49-64 for boys, and 5+50*38 for 

 girls, or 54'64 for boys and 55'38 for girls ; 

 at 10 years of age the mean duration of life 

 is, for boys and girls respectivelv, 10+47-08 

 and 10+47-81, or 57'08 and 57'81; and at 

 30 years of age SO+33'13 or 63' 13, and 

 30 + 34-25 or 64'25. The mean duration of life 

 differs from the mean age at death, inasmuch 

 as the one is a calculation based on all the 

 deaths taking place, after a given age, in the 

 members of a community traced through life, 

 while the other is founded upon such deaths 

 as happen to be noted in a community which 

 has been undergoing continual disturbance by 

 births, immigration, and emigration. 



5. The probable dura/ion of life, probable 

 life-time, equation of life, or vie probable, is 

 the age at which a number of children born 

 into the world will be reduced one-half, so 

 that the chance is equal of their dying before 

 or after that age. Thus it has been ascertained 

 that out of 51,274 males and 48,726 females 

 (making up together the number of 100,000 

 infants) at birth, 25,637 males will die between 

 the 45th and 46th year, or at about 45 years 

 of age, and 24,363 females between the 47th 

 and 48th year, or at about 47 years ; so that 

 the equation of life or probable life-time of 

 males at birth is 45| years, and of females 



* Report, p. xix. 



