FEATURE ARTICLE: WHICH POPULATION TO USE FOR AGE STANDARDISATION?
Age-standardisation is a technique used to enhance the comparability of rates from different populations or different sub-populations over time by making adjustments for the confounding effects of differences in age structure between the populations being compared.
The Australian Bureau of Statistics (ABS) and the Australian Institute of Health and Welfare (AIHW) have previously indicated that the standard population in Australia should be the Estimated Resident Population (Australia's official population estimate) for the years ending in '1' (e.g. 2001 and 2011) and that it should be updated every 10 years.
While following this advice has been accepted practice in Australia in recent years, it is important to note that neither demographic nor epidemiological methodology require the standard population to be updated this frequently. In fact, analysis recently undertaken by a joint ABS-AIHW working group demonstrated that the frequency of the change in the standard population resulted in negligible difference in the comparison of key indicators over time.
The use of age-standardisation in statistical analysis in Australia, particularly involving health and demographic data, has increased substantially. As more age-standardised data are used, and as age-standardised time series become longer, a regular revision to the standard process becomes increasingly more resource-intensive and onerous.
ABS AND AIHW ADVICE ON THE CHOICE OF STANDARD POPULATION FOR AGE STANDARDISATION
The ABS and AIHW recommend that the standard population be revised every 25 years instead of every 10 years, which would reduce the frequency of revisions without reducing the effectiveness of age-standardised comparisons. This would also align the revision cycle with what demographers generally consider to be the timespan of a generation.
STANDARD POPULATION DATA CUBE
To ensure that all age-standardisation is able to effectively reference the same standard population, the ABS has released the data cube 'Standard Population for Use in Age-Standardisation Table' within Australian Demographic Statistics (cat. no. 3101.0), starting with the release on 20 June 2013. It is important to note that these data do not reflect the recasted series, but instead reflect the original final 30 June 2001 population that was published in 2003 and has been used in age-standardised analysis since then.
The ABS and AIHW recommend that the 30 June 2001 standard population in the data cube should be used for age-standardisation until a new standard population becomes available after the 2026 Census.