POST-CENSAL POPULATION ESTIMATES
Estimates of the total population
2.17 Using the Census year (i.e. 30 June) population estimates as the base population, post-censal estimates at the national level are compiled in accordance with births, deaths, and overseas migration. At the state and territory level, an additional item, interstate migration, is included.
2.18 The demographic balancing equation (see paragraph 2.5) describes this process conceptually, however the operational definition used to compile population estimates assumes the error term equals zero.
2.19 The resulting population estimates (Pt+1) then become the base population in the calculation of estimates for the following period. Estimation of the separate components of population change is detailed in Chapter 5 - Estimating births and deaths, Chapter 6 - Estimating net overseas migration and Chapter 7 - Estimating interstate migration.
Population estimates by age
2.20 The procedure outlined above, estimates the total population by updating the base population with the components of population change by sex and financial year of birth, then aggregating to state or territory. This requires data for the components to be classified by financial year of birth in order to match each event to its corresponding cohort in the population. (Population estimates by single year of age at 30 June in effect are a classification of the population according to financial year of birth.)
2.21 Prior to 30 September 2007, classification by financial year of birth was only available for two of the three components of change i.e. births and migration. It was not available for deaths because, apart from a few exceptions (each state and territory has its own notification form), death certificates only required notice of the deceased person's age at the time of death; they did not require date of birth. Knowledge of a person's age is not sufficient information to determine whether that person's birthday has already occurred in the current financial year. Since ABS could not capture information for all states and territories on date of birth of the deceased from death certificates, financial year of birth had to be estimated from age at death.
2.22 The procedures used to create population estimates by age prior to 30 September 2007 can be found in the previous edition of this publication, Demographic Estimates and Projections: Concepts, Sources and Methods, 1999 (cat. no. 3228.0).
2.23 From October 2007, date of birth was available on death certificates from all states and territories, therefore financial year of birth could be calculated for all components of change.