Demography and its theories

Demography is the systematic study of population. The word comes from two Greek words: demos (people) and graphein (to describe). It has two kinds:

• formal demography: the quantitative side, counting and measuring births, deaths and migration;
• social demography: studying the social causes and effects of population changes.

Much of the data comes from the census, a count of every person in a country. The US held one in 1790. In India, a census was carried out between 1867 and 1872, and it has been held every ten years (decennially) since 1881. After independence there were seven, from 1951 to 2011.

Why do numbers about whole populations matter? The sociologist Emile Durkheim studied suicide rates. Suicide seems a very personal act, yet rates differed steadily between groups and countries. So he argued that such aggregate statistics are social facts, explained by social causes.

Malthus's theory (1798): Thomas Malthus said that population grows geometrically (1, 2, 4, 8, 16...) while food grows arithmetically (1, 2, 3, 4, 5...). So population would always outrun food, and 'positive checks' (famine, disease, war) would cut it back. He also suggested 'preventive checks' such as postponing marriage.

Malthus was proved wrong: in Europe, food production grew much faster than he expected, thanks to new technology, and families chose to have fewer children.

The theory of demographic transition links population to development. It has three stages:

The explosion happens because medicine and better food reduce deaths quickly, while people's habits about family size change only slowly.