Technical notes
Youth detention data sources
This report was compiled using 2 data sources. States and territories provided data on the average nightly population per quarter between July 2022 and June 2023. These data were used to supplement the 2021–22 YJ NMDS, which contains data up to and including 30 June 2022 for all states and territories.
This report is not comparable with previous editions of Youth detention population in Australia. Previous editions contained differences in data formats, specifications, definitions and/or quality across jurisdictions. Comparisons between YJ NMDS and youth detention population data should be made with caution.
A data quality statement is available at Youth Justice NMDS 2021–22: Quality statement.
In addition to this report, the Australian Institute of Health and Welfare (AIHW) publishes the annual Youth justice in Australia report series, which provides comprehensive information on young people under youth justice supervision.
The presentation of data in this report is slightly different from the presentation in Youth justice in Australia:
- This report presents the average nightly population for each quarter, while Youth justice in Australia presents the average daily population for each year. These data are reported differently because unit record data are not available for all reporting years for the youth detention population in Australia.
- Young people who are concurrently unsentenced and sentenced are classified as sentenced in this report, but are counted separately as both unsentenced and sentenced in Youth justice in Australia (although they are only counted once in the total detention population in both publications).
This section provides key information about the methods used in this report.
Age
In this report, numbers of young people in detention include all age groups unless otherwise specified. Population rates include young people aged 10–17 only (see ‘Rates’ in this section).
The age on an average night each quarter is calculated based on the age a young person is each night that they are in detention. If a young person changes age during a period of detention, then the average nightly number in detention will reflect this.
For example, where a young person turns 18 during a period of detention, any nights spent in detention (sentenced or unsentenced) aged 18 will be counted only in quarterly average nightly population for the 18+ age group. Similarly, nights spent in detention before a young person has turned 18 will be counted only in the 10–17 age group.
Average nightly data broken down by age are not comparable to Youth detention population in Australia releases prior to 2020.
Average nightly population
The average nightly population is calculated by adding the duration (in nights) of each period of detention that falls within the quarter, and dividing the summed duration by the number of nights in the quarter.
Indigenous status
Information on Indigenous status has been collected since the implementation of the YJ NMDS. The AIHW uses 'First Nations people' to refer to Aboriginal and Torres Strait Islander people in this report.
Nationally, the proportion of young people with ‘not stated’ Indigenous status was between <0.2% and 1.0% each quarter between the June quarter 2019 and the June quarter 2023. This proportion was low (2.3% or less each quarter) in all states and territories.
Changes in the collection and recording of Indigenous status can affect rates of First Nations identification over time.
There are some differences in the ways states and territories collect information about Indigenous status. Not all jurisdictions use the national standard question and standard codes for recording Indigenous status, as recommended by the Australian Bureau of Statistics. Some jurisdictions have taken steps to improve their data collection forms and information systems in recent years to address this issue.
Legal status
Young people who are both sentenced and unsentenced at the same time (that is, serving multiple or concurrent supervision orders) are classified as ‘sentenced’ in this report.
Population rates enable different groups to be compared, while taking into account different population sizes. Because there are differences between the states and territories in the extent to which young people aged 18 or over can be detained in youth justice facilities, rates are restricted to those aged 10–13, 14–17 and 10–17. Crude rates are presented in this report.
The number of young people in detention on an average night during a quarter is rounded to the nearest person in text. The rate is calculated using the number on an average day before rounding.
In the text of this report, rates are presented to one decimal place for rates less than 10, and to the nearest whole number for rates 10 and over. Rates are presented to 3 decimal places in the supplementary tables. As a result, rates calculated by using the average nightly population rounded to whole numbers might differ slightly from the rates presented in this report.
Due to a lack of statistical reliability, rates are not calculated where there are fewer than 5 young people in the numerator. In some instances, the number of young people might be presented as 5, but the rate might not be calculated due to rounding (for example, if there are 4.7 young people in detention on an average night, this will appear as 5 in the table, but the rate will not be calculated). But these young people contribute to overall state and national rates. The calculation of rates for young First Nations and non-Indigenous Australians excludes young people with unknown Indigenous status.
Population data used in the calculation of rates are provided in the supplementary tables S55a, S55b and S55c.
Rates for different groups can be compared using a rate ratio, which is the ratio of 2 rates.
In this report, rate ratios are used to compare First Nations and non‑Indigenous rates, and to provide a measure of the level of First Nations over‑representation. Rate ratios are calculated by dividing the First Nations rate by the non-Indigenous rate.
Rate ratios should be interpreted with caution where there are small denominators, rare events, and rates that converge while declining.
Due to a lack of statistical reliability, rate ratios in this report are not calculated where one or both of the rates have fewer than 5 young people in the numerator. However, these young people contribute to overall state and national rate ratios.
The average nightly population is rounded to whole numbers using numbers presented in the supplementary tables at 3 decimal places, so components might not sum to the totals.
Rate ratios were calculated using rates rounded to 3 decimal places. Proportions were calculated using average nightly numbers rounded to 3 decimal places. Numbers and rates displayed in figures are rounded, as presented in the supplementary tables.