The crude birth rate is the number of live births per year, per 1 000 population. This does not take the age structure of a population into account, and hence the numbers of women who are capable of giving birth in any year, making accurate comparisons difficult. Because of this, many demographers prefer to use a standardized birth rate which indicates what the crude birth rate would have been for a population if the age and sex composition of that population were the same as in a population selected as standard, allowing comparisons to be made between geographical areas, or across social groups within a society (see Fargues (1997) Pop. & Dev. Rev. 23, 1 for a demonstration of standardization).