An important measure of death, or of life, is the life-expectancy . This can be calculated from a life-table. An interesting, and albeit significant, measure of death is the cause-specific death rates. By analyzing these rates over time, a demographer can understand the reasons for mortality in a population. The measures of compositions of populations are usually the most interesting.
Demographers study age compositions, usually by age groups.
They can also study the dependency ratio , which is the number of children and elderly compared to the number of working-aged adults. Another measure is the children to elderly ratio. By observing this ratio, demographers can tell if a population is young or old, and what implications it has on future social programs. Demographers also study sex composition, like the sex ratio . This ratio tells of the number of men to women, which is especially important in the age-groups when populations begin marriage.