Population.— This is the first fact which will be sought in preparing the vital statistics of any conununity. It is obtained by the cen sus which is taken once in 10 years by the nation, once in five years or oftener by some of the States and cities. It is inaccurate in vari ous localities, sometimes from the dishonesty or incompetency of the enumerators and some times from the fault of those from whom infor mation is sought Revision of the last census in many of the cities and towns showed remark able variations from the figures which had been obtained by the official gatherers. When the population of two or more places is known we have the first factor or element for making comparisons between these places.
In the interval or intercensal years, when a direct count is not taken, an increase of popula tion is usually pre.supposed, and is estimated by comparison of the two previous census enumera tions. This is an inaccurate method, further more a decrease instead of an increase is often !mown to be the fact. Increase of population, for a given period, is due to the excess of births over deaths, as recorded in the archives of the board of health, or other office of regis try, and to this must be added the excess of those who come into a community over those who leave it Diminution of population is due to excess of deaths over births and to removals from the community.
Population may increase slowly or rapidly and is greatly influenced by prosperity. or the reverse, by sickness, by climatic conditions or hy the advantages or disadvantages of residence in the given conununity.
Make-up of population refers to the relative numbers of males and females, and their ages. It also includes details as to color or race, and nationality. In many communities, especially in those which are large and highly organized, there is an excess of females over males. This is especially apt to be the case in manufacturing communities, while in pioneer settlements there is always an excess of finales. In villages and small towns, especially in farming communities with their preponderance of outdoor worlg this is also the case.
Age statistics are usually arranged according to decades, except that the infant population in cludes those who are under one year of age. Still-births, of coarse, make no addition to the population, but a record of them is important for it may lead to deductions which are of great significance for a given community. Age statistics have a very important relation to mortality statistics. The highest mortality rate is in infancy, and as this rate in some localities is extreme, it should call for study and invese gation in such localities, especially when the total mortality rate is unusually high.
Color is an important detail in the records of population. There are many communities in which there is but one color, black, white, red or yellow, but on the other hand the United States is a very composite nation, and hence there is a very positive necessity for the color distinction for a large portion of the popula tion. The statement ap.plies even to a greater degree in reprd to nationality. As there may be 20 or more nationalities in a single city the necessity for classification is apparent enough.
The sparse population in certain farnung districts, especially in the less fertile or the newly-settled portions of the 'country, or in those which are unfavorably located from sani tary or commercial conditions, the crowded pop ulation of the great cities where opportunities for labor are abundant, the overcrowding of the slums and the abnormal housing of multitudes of human beings in many of the factory cities and villages furnish material for vital statistics which are invaluable from a sociological stand point They .are also the basis of some of the most educaung calculations with regard •to mortality and morbidity mtes.
The rule was formerly accepted by statisti cians as generally applicable that the greater the density of population the higher the death mte, but the many sanitary improvements in housing arrangements in recent .years, especially in localities where the density of population is great, have considerably modified this rule. The m6rtality rate in such localities is now meth lower than it was a few years ago and this improvement applies not to the United States only but to the civilized world. (Public health is purchasable. Twenty-five thousand lives can be saved in New York State within the next five years?' (H. M. Biggs, commissioner of health of New York.) Statistics in regard to population are taken periodically or intermittently, while those which relate to birth, death, marriage and disease, which are sometimes called registrar's returns, are constantly in the process of niaking. Every community, large or snail, has them as an essential portion of its records or archives. In the record of diseases, especially those which are of an infectious or contagious character, the list is increasing from year to year. It is easy to see that many valuable deductions and com parisons can be made from such records, es pecially in regard to sanitary and hygienic im provements. In all places of any considerable size they are now under the control of boards of health which are usually endowed by the legislatures with ample legal powers.