demography

n. study of the vital statistics of a population (i.e. deaths and birth)

Demography is the statistical study of all populations. It can be a general science that can be applied to any kind of dynamic population, that is, one that changes over time or space (see population dynamics). It encompasses the study of the size, structure and distribution of populations, and spatial and/or temporal changes in them in response to birth, death, migration  and aging.
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Demography /de·mog·ra·phy/ the statistical science dealing with populations, including matters of health, disease, births, and mortality. [more]Demography - Community and Resources

Noun
1. the branch of sociology that studies the characteristics of human populations
(synonym) human ecology
(hypernym) sociology

(n.)
The study of races, as to births, marriages, mortality, health, etc.