7.3 Period information - information from a certain time period

Population change data concern a certain time period, often a year. Such data can be births and deaths during the year. Period information is very central when calculating key ratios as they describe the frequency of population changes occurring over the year.

Population changes can be examined for a longer time period than one year. Then it is common to use a five-year period. A ten-year period is also employed.

As a rule of thumb, key ratios are calculated for a period of one year because in demography data for different years are often compared with one another.