Age and Sex Structure of A Population
Armed with these data, the tasks of a demographer are to describe the composition and understand the dynamics of a population. In doing so, demographers pay particular attention to two variables: age and sex. Age and sex are both the cause and effect of many demographic trends: for example, the number of women aged 20-24 in 2005 in the US depends on 1) the number of births that have occurred between 1981 and 1985 in the US, 2) the number of these births that have survived to 2005 or have not moved out of the US between their birth and 2005, and 3) the number of women aged 20-24 who immigrated into the US after their birth. On the other hand, the number of women aged 20-24 in 2005 also determines how many births there will be in the US population in 2005. As you can see, age-sex structure of a population and demographic trends are closely intertwined.