Complete the account of the basic demographic measures.

A crude birth rate is expressed per 1,000 of the whole population, which makes it sensitive to age structure. The total fertility rate avoids that by summing age-specific rates for a single year. In a low-mortality country the replacement level is about 2.1 children per woman, and the ratio of the young and the old to those of working age is called the dependency ratio.

The word "crude" is doing real work: it is a warning label. Two countries with identical childbearing behaviour can show crude birth rates that differ by half simply because one has more women of childbearing age, which is why any comparison across countries or decades should reach for the age-specific measure.