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1. 'Age' is one of the basic demographic variables used in population statistics. It is widely used in cross classification with other variables such as sex, marital status, occupation etc. It is most commonly used to differentiate populations in terms of the time elapsed (usually in complete years), generally from date of live birth to a point in time (e.g. date of a particular survey). Depending on the population, or topic of study, age may be measured in different 'time units' (e.g. infants under one year are measured in completed days, weeks and months and for persons over one year, in complete years).

2. Although most data on age refer to living persons, some collections provide data on the age of deceased persons.

3. The meaning and description of the concept are generally standard in the Australian Bureau of Statistics (ABS) and other organisations. However, there is considerable and legitimate variation in output categories, directly linked to particular survey populations or topics. For example, interviewing for Labour Force Surveys is restricted to persons 15 years and older, and surveys concerned with perinatal deaths require age in terms of minutes, hours and days. Other examples include 'neonatal deaths' and 'births by age of mother'.