About the data

3.3        There are two distinct data sets: ‘stock’ and ‘flow’. In short, flow

describes the characteristics of offenders sent to prison. The stock profile describes the characteristics of those in prison … minor offenders generally end up accounting for a much smaller proportion of the prison stock than of the prison flow.[18]

Data representing the ‘stock’ prison population

3.4        To provide the ALRC with an analysis of the ‘stock’ prison population, Curtin University used available and requested data from the annual census, Prisoners in Australia (ABS PIA), collected on 30 June each year and published by the ABS.[19]

3.5        ‘Stock’ data was used to show Aboriginal and Torres Strait Islander over-representation in the national prison population generally, and in the remand population. It was used to show sentence length for those in prison on census night, and to calculate prior imprisonment rates.

Data representing the ‘flow’ prison population

3.6        To provide the ALRC with an analysis of ‘flow’, Curtin University used data from the ABS Criminal Courts Australia series (ABS CCA).[20]

3.7        Prison receptions were approximated from the ABS CCA data by counting the number of defendants in a period that were handed a custodial sentence by the courts.  Although these custodial terms may not be served in the same period that the sentence was handed down, the commencement date was sufficiently close to allow for reasonable approximation. In addition, counting rules regarding the determination of ‘principal offence’ in court finalisations were not entirely the same as those used to determine ‘most serious offence’ in prison statistics; however, these were also sufficiently similar to allow comparison. Sentence quantum, as handed down by the court and described in ABS CCA publications (often referred to as ‘head sentence’) was also sufficiently similar to the ‘aggregate sentence’ in ABS PIA statistics to allow comparison.

3.8        Although presented as a national series, breakdowns by Aboriginal and Torres Strait Islander status from the ABS CCA were only available for selected jurisdictions—New South Wales (NSW), the Northern Territory (NT), Queensland and South Australia (SA). For other jurisdictions,[21] court finalisation statistics did not provide information about the Aboriginal and Torres Strait Islander status of defendants. When combined, NSW, the NT, Queensland and SA account for more than three-quarters of the Aboriginal and Torres Strait Islander general population in Australia and 60% of the non-Indigenous general population. Given this coverage, it was possible to use the available data to make reasonably accurate assessments of national trends.

3.9        The exclusion of Western Australia (WA) from ABS CCA most likely yielded an under-estimate of the true national rate of Aboriginal and Torres Strait Islander court finalisations, given the typically high level of Aboriginal involvement in the WA criminal justice system and the use of short prison terms to pay off fines.[22]  ABS CCA also excludes traffic related offences,[23] which likely further contributed to an under-enumeration of national prison receptions.

3.10     ‘Flow’ data was used to show Aboriginal and Torres Strait Islander over-representation rates. It was further used to show the charges that were before the courts, conviction rates, and the penalties imposed for both Aboriginal and Torres Strait Islander offenders and non-Indigenous offenders. It was also used to show the type of offences that led to imprisonment, and to illustrate sentence lengths for those prisoners who may not have been in prison on census night.

3.11     Across both data sets, where offence categories are cited, they are categorised using the Australian and New Zealand National Standard Offence Classification.[24] Only the most serious offence for each prisoner is published in the ABS PIA series.

3.12     There are limitations to the data used to inform this chapter. These are discussed at the end of the chapter, along with data limitations that may affect understandings of Aboriginal and Torres Strait Islander incarceration more broadly.