AGE STANDARDISATION

Age standardisation is a way of allowing comparisons between two (or more) populations with different age structures, for a variable related to age. The age standardised estimates are not useful on their own, but the comparison between two (or more) age standardised estimates can remove the confounding effects of age.

Age standardisation may be considered for comparison between populations in the following scenario:

• the variable of interest is strongly related to age;
• the age structure between the populations of interest is quite different;
• the aim is to measure differences between the populations other than those caused by age structure; and
• a summary measure is required to describe the differences, rather than a detailed breakdown by age.

Age standardisation is only appropriate when the following assumptions are met:

• the age structures of the populations being compared are different;
• the variable being compared is strongly related to age, and there are no other confounding variables; and
• the relationship with age and the variable of interest is broadly consistent across the populations being compared.

If the assumptions above are not met, a more appropriate method for comparison between populations would be to compare the distribution of the variable of interest by age group. For example, unadjusted (non age standardised) data could be output in 10-year age ranges.

Age standardisation techniques were applied to some data in the 2014–15 NATSISS summary publication to remove the effect of the differing age structures for comparisons between Aboriginal and Torres Strait Islander, and non-Indigenous populations. The age structure of the Aboriginal and Torres Strait Islander population is considerably younger than that of the non-Indigenous population. The age standardised estimates are those rates that 'would have occurred' should the Aboriginal and Torres Strait Islander and non-Indigenous populations both have the standard age composition.

The method used to calculate age standardised rates is explained in Reliability of estimates (Technical note), released with the 2014–15 NATSISS summary publication.