Practical preventive medicine . per cent. IB 50 per cent and over. The heavy lines (?») show geographic divisions. Pig. 125.—Percentage negro in total population by states, 1910. Bur. Census.) (Bull. 129. populations. Distinction is upon a purely arbitrary in the 1870 census towns of 8000 population or less wereconsidered rural, in 1880, 4000 or less and in 1910, 2500 or it can be seen that these distinctions have not been madeon a constant basis. In the 1870 census per cent, of thecountrys population was urban and in the 1880 census percent. 6. Another importan
Practical preventive medicine . per cent. IB 50 per cent and over. The heavy lines (?») show geographic divisions. Pig. 125.—Percentage negro in total population by states, 1910. Bur. Census.) (Bull. 129. populations. Distinction is upon a purely arbitrary in the 1870 census towns of 8000 population or less wereconsidered rural, in 1880, 4000 or less and in 1910, 2500 or it can be seen that these distinctions have not been madeon a constant basis. In the 1870 census per cent, of thecountrys population was urban and in the 1880 census percent. 6. Another important point is the determination of thedensity of population, that is, the number of individuals perunit of surface area. Most commonly for larger areas suchas states and countries the population is divided by the totalarea in miles or acres (Fig. 126). For comparative studies in an STATISTICS OF POPULATION 3°9 urban population it is perhaps better to analyze data accordingto ward populations rather than by density per In considering population fluctuations within civil areas insuccessive years it is important to ascertain if any changes havebeen made in the geographical boundaries of the area under con- 310 PRACTICAL PREVENTIVE MEDICINE sideration. Large increases may be due to the annexation ofterritory with a considerable population, and sudden increasesthus appear. 6. Value of Vital Statistics.—In any consideration of variousfacts concerning a large body of individuals, such as the popula-tion of a city, a state or a nation as regards births, deaths orindividuals, it is impossible to consider the individual by him-self, but rather all must be considered in the aggregate if anyclear conception is to be gained of the influence of economic ormorbific factors. Considered as individuals we would losesight of the mass. As a consequence, it is necessary to employstatistical methods to avoid confusion and to enable the trendof events to be clearly discerned. In any employm
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