MORTALITY, a term applied to that branch of investigation which determines the proportion of the number of persons who die in any assigned period of life or interval of age, out of a given number who enter upon the same interval, and consequently the proportion of those who survive. Tables showing how many out of a certain number of infants, or persons of a given age, will die successively in each year till the whole become extinct, ate generally called tables of mortality. There is no fixed number of lives upon which such tables are based, but the observation of a large number is indispensable to accuracy, and the larger the number that can be duly observed the greater will be the degree of accuracy attained. It must always be borne in mind, however, that a strict observation of a moderate number will yield truer results than a looser induction from a larger number. The basis of such calculations must be an accurate register of the number of births and deaths, and in the case of the latter, at what ages, in a given district or extent of country.
In Great Britain the bills of mortality, or abstracts from parish registers, were long the only means of arriving at these results; but being found very imperfect and unsatisfactory, they were supplanted in 1836 by a general regis tration. The results furnished by such tables are very various and of great interest. The registers, if kept with sufficient accuracy and minuteness, enable us to determine the propor tion of deaths, not only at different ages and in different regions, but at different seasons, in persons of different occupations and habits, in towns or the country; and thus afford valu able materials for the science of political econ omy. Although much more attention has been to this subject in recent times, yet the observations have not been so extensive nor so accurate as is desirable.
Although the collection of regular statistics of mortality is of recent origin, the subject has always excited much interest, and many general facts have been collected regarding it. The tendency of mortality to diminish with the progress of civilization has been satisfactorily established by statistics. The average rate of mortality is affected by regular or constant causes, such as race, climate, age, sex, profes sion, social position, density of population, political institutions, habits, etc., and by such irregular or occasional causes as war, famine, pestilence, etc., but notwithstanding the inter ruption of these occasional causes a constant tendency to a mean has been found to exist in any given state of society. The fact that the tendency of population to increase or diminish is quite independent of the rate of mortality was first established by Malthus, who showed that the increase of population depended on the facility of procuring the means of sub sistence and not on the duration of life. The
mortality in the United States, for example, is greater than in England, yet the population of the United States doubles itself in 25 years and that of England in 43 years, while in vari ous European countries which have a lower mortality than the United States, the population will not double in a century.
Some statists have attached considerable im portance to the effects of race on population. It is extremely difficult, however, to establish anything in regard to race independently of circumstances and social habits. It has been shown, for example, that the average mortality among the Jews in Prussia is less than among the Christians, that the mortality varies greatly among the various races who inhabit the Aus trian Empire, being least among the Germans, and that a similar difference prevails in the de partments peopled by various races in France, but all such evidence is open to the most obvious exceptions. The influence of climate on mor tality is inseparably associated with that of migration. It cannot be established that any climate, except perhaps the extremes of heat or cold, moisture or dryness, is in itself exception ally favorable or unfavorable to human life, but change of climate is frequently adverse to it.
The most remarkable fact in respect to age is the great mortality which commonly takes place amongchildren under five years of age. This is especially remarkable in large towns, but is not wholly confined to them. Although the diseases to which infancy is liable may naturally account for part of this excessive mortality, the greater part of it must be at tributed to ignorance and want of due care in the training of children, partly arising from the unfavorable circumstances in which, through the too rapid increase of population, they are brought into the world. This is both directly and indirectly a considerable cause of the extra mortality of large towns and other dense cen tres of population. The question whether city or country life is most conducive to a low rate of mortality is still undecided. Direct statistics prove nothing, as the death rate of towns is raised by immigration from the country and other causes. In regard to sex it is established that women live longer than men, and that among men the married live longer than the single. The condition of life in respect of poverty or wealth is known to have a consid erable influence on mortality. Dividing France into two classes, rich and poor, the annual mor tality was found to be 1 in 46 in the former and 1 in 33 in the latter. This gave to the rich an average duration of life of 57 and to the poor one of 37 years. See LONGEVITY; VITAL. STATISTICS.