Crime and Criminal Justice Statistics

AIC policy on calculating rates for Indigenous people

The Australian Bureau of Statistics uses two methods to estimate Indigenous populations: "low series" and "high series". Both employ certain assumptions about births, deaths and migration. The high series assumes a more rapidly increasing population (an annual average rate of 5.3% per year) based on the increasing number of persons who self-identified as Indigenous between 1991 and 2001 as well as natural growth (births and deaths). The low series provides for a more conservative population estimate, projecting an average increase in the Indigenous population of only 2.0% per year, which can be attributed to natural growth.

Rates of crime and incarceration for Indigenous people will differ depending on which population estimates are used. High series data provide a larger base population compared to low series data, and will therefore result in lower rates. Analysts must therefore be cautious when calculating rates for Indigenous people, as rates and over-representation ratios will differ depending on whether high or low series data are used.

Arguments can be made for using either the high or low series data to calculate Indigenous rates. Whereas the ABS uses low series, the AIC uses high series data as it produces a more conservative estimate of incarceration rates and overrepresentation ratios. Further, since high series data have been used by the AIC in the calculation of rates since 1991, it is the policy of the Australian Institute of Criminology to continue to use high series population data for the calculation of crime and incarceration rates for Indigenous people for the purposes of maintaining consistency and integrity with previously published data. A shift to low series data in AIC publications, either on a temporary or longer-term basis, would result in difficulties with interpretation and inconsistencies with past publications.

Indigenous population data are derived from the 'Experimental projections of the Aboriginal and Torres Strait islander population' publication (ABS cat. no. 3231.0).