Period and cohort data
Demographic analysis may use either cohort or period data.
Period data
Period data are events which occur during a set period of time, often either one year or five. Period data contains the demographic experiences of people of many different ages (in other words, people belonging to many different birth cohorts). Many of the commonly used demographic rates are based on period data, such as crude birth rates.
1. Advantages of using period data
- Period data are easy to collect.
- Period analysis can use the most up-to-date information and thus be used to measure current trends.
- Period analysis is useful for when we wish to show rapid fluctuations which are a response to social, political or cultural events.
2. Disadvantages of using period data
- The summary rates calculated from period data do not represent real life experiences. Over the course of an individual’s life the rate of occurrence of demographic events will change.
- Period analysis is subject to tempo effects. This will be covered in greater detail in Session 4 (Measuring fertility).