332 



Ml'. Lubbock on the Comparison of 



4. Tables of mortality which are founded upon registers of 

 deaths only are subject to an error arising from the supposition 

 that the population is stationary, as was long ago noticed by 

 Dr. Price, Vol. II. p. 2.51. 



The probability of an individual dying in a given w'" year 

 of his life, if the effect of migration be neglected, is the number 

 of deaths of that age divided by the number of births in one 

 year, n years previously, which, if the population were stationary, 

 would be the same as the total of deaths in any year. 



If therefore the births n years previously are than the 



total of deaths at all ages in the year of the observation, the 



probability of an individual dying at the n'" age is ^ than the 



quotient of the deaths at that age divided by the total of the 

 deaths at all ages. In America this effect is I think clearly 

 perceptible, and has led some persons to conclude that the popu- 

 lation in that continent is more unhealthy than in Europe. 



The following Table has been formed from the Bills of 

 Mortality for Boston, New York, Philadelphia and Baltimore 

 in 1820 



Expectation of Life at Birth 24.959, 



which Table is much lower than any of the others, but the 

 annual rate of increase of the population in the United States 

 between 1810 and 1820 was about 1.034. In England at the 



