INTRODUCTION

2.1 Population estimates by sex for Australia and each of the states and territories are published quarterly as at 31 March, 30 June, 30 September and 31 December in Australian Demographic Statistics (cat. no. 3101.0). Estimates by single year of age and sex are compiled quarterly but are only published annually as at 30 June in Population by Age and Sex, Australian States and Territories (cat. no. 3201.0).

2.2 Two main steps are involved in estimating the national and state/territory population:

• calculating the base population (Census year population estimates)
• updating this base population (post-censal population estimates).

2.3 The post-censal population estimates are derived by bringing forward the base population by ageing the base, then adjusting for subsequent components of population growth, i.e. births, deaths, overseas and interstate migration. This method is called the cohort component method.

2.4 Population estimates are referred to as either preliminary, revised or final. Preliminary estimates are generally made available 5 to 6 months after the reference quarter. Revised estimates are generally published each March for the financial year ending 21 months previously (e.g. revised estimates for the 2006-07 financial year were available in March 2009). Final estimates are published for the previous five-yearly intercensal period after each Census.

2.5 The following equation is known as the demographic balancing equation (Shryock, Siegel and Associates, 1976) and is used to update the base population.



where:

2.6 As complete component data (births, deaths, net overseas migration and net interstate migration) is often not available at the time an estimate is compiled, a residual error is included. This residual error encompasses measurement error for the components of population growth (births, deaths, overseas and interstate migration). The residual error can only be measured after each Census, and is referred to as intercensal discrepancy (see below).

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