Age-sex structures and population pyramids
Describing populations
Population stock refers to the composition of a population at a given point in time. While this can be broken down into many components, such as religion, marital status, ethnicity etc, demographers are primarily interested in the age-sex structure of a population. This is because the age-sex structure of a population is a fundamental determinant of the numbers of demographic events that will occur, as well as determining the types of services a population will need e.g. schools, care homes, maternity services etc.
The age-sex structure of a population is simply the distribution of the population by age and sex. It may be described in terms of absolute numbers or percentages.
Because of the importance of the age-sex structure as a starting point for demographic investigation, a specific way of depicting them graphically has been developed. These depictions of age-sex structures are called population pyramids. The next section will describe how a population pyramid is constructed.