The Juvenile Justice National Minimum Data Set (JJ NMDS) contains information on all children and young people in Australia who were supervised by youth justice agencies in the community and in detention.
Data are extracted from the administrative systems of the state and territory departments responsible for youth justice in Australia.
Overall, the levels of missing data in the JJ NMDS are low. Less than 7% of all young people in the JJ NMDS since 2000–01 have an unknown Indigenous status, and similar proportions of records in each of the order (7%) and detention (6%) files have unknown or missing information for the postcode and suburb of the young person’s usual residence. For all other variables in the JJ NMDS, the proportion of missing data is 1% or less.
In particular, the Northern Territory did not provide JJ NMDS data for 2008–09 to 2015–16. In 2015–16, the Northern Territory provided non-standard data for the period 2011–12 to 2015–16. Therefore, many data tables contain two totals:
In addition, not all participating states and territories were able to provide JJ NMDS data in the current format for all years of the JJ NMDS (2000–01 to 2015–16). Some trend analyses exclude those states and territories with incomplete data in the new format due to comparability issues.
In New South Wales, responsibility for the Kariong Juvenile Justice Centre was transferred from the NSW Department of Juvenile Justice to the NSW Department of Corrective Services on 10 November 2004, and it was renamed the Kariong Juvenile Correctional Centre. As the JJ NMDS includes only young people who are supervised by youth justice agencies in Australia, information about young people in custody in the Kariong Centre after 10 November 2004 is not included. In 2012–13 there were 28 young people on an average day in the Kariong Centre, and therefore they formed only a small proportion (around 8%) of young people in detention in New South Wales.
Kariong Juvenile Correctional Centre was closed in early 2015. During April and May 2015, 23 young people were transferred out of the Kariong Centre to another youth detention centre under the supervision of Juvenile Justice NSW. All young people under the age of 18 years who were transferred out of the Kariong Centre, and who entered the supervision of Juvenile Justice NSW, entered the JJ NMDS data collection on the date they were transferred.
The 2015–16 reporting period is the first year to include JJ NMDS data from Western Australia since 2007–08. For the 2015–16 collection, the Western Australia data supply included only the sentenced detention period, where a young person was both sentenced and unsentenced at the same time. As a result, there may be an undercount of young people on unsentenced detention orders.
South Australian data reported in 2015–16 may vary from that reported in previous years due to improvements in data quality and assurance.
For Tasmania, complete data on detention periods and orders are available only for 2006–07 onwards. Because data on length of detention is used to derive the time spent under community-based supervision, information on periods of community-based supervision before 2006–07 may therefore be incomplete and are not reported.
For the Australian Capital Territory, data for 2000–01 to 2002–03 are not available and data for 2003–04 to 2007–08 are available only in JJ NMDS 2007 format. Some trend analyses therefore exclude the Australian Capital Territory.
In the Australian Capital Territory, both police-referred pre-court detention and remand (court-referred detention) are recorded as remand.
The end reasons for orders are not available for the Australian Capital Territory.
The Northern Territory did not provide JJ NMDS data for 2008–09 to 2015–16. Limited data in a non-standard format were provided for 2011–12 to 2015–16. These data are included in the analyses where possible.
Data for 2007–08, which are the most recently available JJ NMDS data for the Northern Territory, are used in the national totals for 2008–09 to 2010–11 where possible, but are not reliable enough for separate reporting.
Data for 2000–01 to 2007–08 are available only in JJ NMDS 2007 format. Some trend analyses therefore exclude the Northern Territory.
Less than 7% of all young people in the JJ NMDS since 2000–01 have an unknown Indigenous status. In 2015–16, less than 3% of all young people under supervision during the year had an unknown Indigenous status. Among the states and territories, this ranged from less than 1% in Victoria (0.3), Western Australia (0), South Australia (0.4) and Tasmania (0.4), to 8% in New South Wales.
In Youth justice in Australia reports, young people with ‘not stated’ Indigenous status are excluded from analyses of Indigenous status data.
In 2011, an AIHW review of Indigenous data quality in the JJ NMDS found that there were variations among the states and territories in the use of the Australian Bureau of Statistics standard for collecting and recording Indigenous status data. See the report Aboriginal and Torres Strait Islander identification in community services data collections: an updated data quality report, IHW 80 for more information.
Age is calculated as at the start of the first relevant period of supervision unless that period of supervision began before the financial year, in which case age is calculated as at the start of the financial year. A young person's age can therefore vary across tables as age is calculated in respect to the type of supervision being analysed. For example, a young person enters supervised bail aged 17 on 1 August and leaves on 30 August. They turn 18 on 15 September, enter sentenced detention on 1 December and are released on 1 January on parole, which ends on 30 January. They have no other periods of community-based supervision during the financial year.
This means that for a particular age group, the total number of young people under supervision may not be the sum of the number of young people under particular types of supervision.
Across Australia, young people may be charged with a criminal offence if they are aged 10 or older. The upper age limit for treatment as a young person is 17 (at the time an offence was allegedly committed) in all states and territories except Queensland, where the age limit is 16. Young people aged 18 and older (17 or older in Queensland) at the time an offence was allegedly committed are dealt with under the criminal legislation relating to adults.
However, it is possible for young people aged 18 and older to be under youth justice supervision. Reasons for this include the offence being committed when the young person was aged 17 or younger, the continuation of supervision once they turn 18, or their vulnerability or immaturity. In addition, in Victoria, some young people aged 18—20 may be sentenced to detention in a youth facility (known as the 'dual track' system).
Two measures of central tendency are reported using data from Juvenile Justice National Minimum Data Set (JJ NMDS):
The JJ NMDS contains information on the start and end of supervised orders that youth justice agencies administer and on the start and end of detention periods. As the start and end dates in the JJ NMDS do not include time stamps, a young person is counted as being under community-based supervision for any day that is covered by a community-based supervised order and is not covered by a detention period. In some circumstances, the young person is considered to have moved between community-based supervision and detention on the same day and is counted as having both types of supervision:
See also Supervision periods.
Duration is calculated in whole days. For example, if a young person entered supervision on 1 January and left on 5 January, this is counted as 5 days under supervision, while if a young person entered and left supervision on the same day, this is counted as 1 day under supervision.
The JJ NMDS contains the date on which the youth justice agency first supervised or case managed each young person under supervision. This date is used in analyses of age at first supervision.
In contrast to the age at first supervision, analyses of the first type of supervision and supervision history are restricted to those young people for whom information on this first supervision is available in the JJ NMDS. For all states and territories except Tasmania and the Australian Capital Territory, information on the first type of supervision is available for all young people whose first supervision was on or after 1 July 2000; for Tasmania, this is 1 January 2006 (as complete data on detention are available only from this date); for the Australian Capital Territory, this is 1 July 2008 (as data for 2003–04 to 2007–08 are available only in JJ NMDS 2007 format).
The first supervision type is determined for each young person with available data by selecting the records with the earliest start date. Because it is possible for young people to be under more than one type of supervision at the same time, young people may have multiple first supervision types.
A young person's supervision history is composed of all available information in the JJ NMDS, up to and including the current reporting year. Only young people with information from their first supervision are included in this analysis.
In 2015–16, the Northern Territory provided non-standard data for the period 2011–12 to 2015–16. Therefore, many data tables contain two totals:
Comparisons between JJ NMDS and non-standard data should be made with caution due to potential differences in data format, specifications, definitions and/or quality.
Reports based on the JJ NMDS contain information on both the number of young people under supervision on an average day and the number of young people under supervision during the year.
The average day measure reflects the number of young people under supervision on a typical day during the year, and gives an indication of the average number of young people supported by the supervision system at any one time. It is a summary measure which reflects both the number of young people supervised, and the amount of time they spent under supervision. This measure is the main focus of most JJ NMDS data. In contrast, the 'during the year' measure is a count of the number of unique individuals who were supervised at any time during the year.
Comparing the two measures provides information on the average length of supervision during the year.
Both the average day and during the year counts are provided in most supplementary tables, where appropriate.
The number of young people under supervision on an average day is calculated by summing the number of days each young person spends under supervision during the year and dividing this total by the number of days in the financial year.
For the number on an average day, components may not sum to the total because:
For example, if there are 3.4 young women on an average day and 3.4 young men on an average day, the total is 6.8 young people. When these numbers are rounded, the corresponding table would show 3 young women, 3 young men and a total of 7 young people.
The number of young people under supervision during the year is calculated by counting each distinct young person under supervision during the financial year. Each young person is counted only once, even if they entered and exited supervision multiple times during the year.
For the number during the year, components may not sum to the total because:
For example, if there were 100 young people under supervision in a particular year and each of these 100 young people had been detained and under community-based supervision at different times during the year, the relevant totals would show that there were 100 young people in detention, 100 young people under community-based supervision and a total of 100 young people under supervision.
Similarly, a young person may be 15 years at the start of their first period of detention during the year but 16 years at the start of their first period of community-based supervision. This young person would appear as a 15-year-old in detention tables but as a 16-year-old in community-based supervision tables, and as a 15-year-old in tables for the total number under supervision.
While the number of young people under supervision varies by state and territory, so does the total number of young people who live in that state or territory. To compare the number under supervision while taking into account differences in population sizes, population rates are presented using data from the Australian Bureau of Statistics (ABS). Population rates are calculated by dividing the number of young people under supervision by the number of young people who are eligible to be supervised. Those who are eligible must relate to those under supervision (that is, if the rate is calculated for males under supervision, then those who are eligible can only be males).
Population rates are calculated for both the number under supervision during the year and the number under supervision on an average day. Because there are differences between the states and territories in the extent to which youth justice agencies can supervise young people aged 18 and older, all rates are calculated for those aged 10—17. This number is then multiplied by 10,000 (although any multiplier could be used). The rate can then be expressed as the number per 10,000 young people. For example, if there were 10,000 young people aged 10—17 under supervision during the year and there were 2,000,000 young people aged 10—17 in Australia, then there were 50 young people under supervision for every 10,000 young people aged 10—17 in Australia (or 0.5% of the population aged 10—17). Similarly, if there were 5,000 Indigenous young people aged 10—17 under supervision in Australia and there were 100,000 Indigenous young people of this age in Australia, then there were 500 Indigenous young people under supervision for every 10,000 Indigenous young people aged 10–17 years in Australia (or 5% of the Indigenous population aged 10—17).
The calculation of rates for Indigenous and non-Indigenous young people excludes young people with unknown Indigenous status. Rates are not calculated where there are fewer than 5 young people due to a lack of reliability.
The number of young people on an average day is rounded to the nearest whole person. The rate for an average day is calculated using the number on an average day before rounding.
Rates can be compared using a rate ratio, which is the ratio of two rates. Rate ratios should be interpreted with caution where there are small denominators, rare events and rates that converge while declining. In JJ NMDS reporting, rate ratios are mainly used to compare Indigenous and non-Indigenous rates and to provide a measure of the level of Indigenous over representation. Rates are also presented to guide interpretation.
Rate ratios are calculated using the rates to two decimal places, as published in the supplementary tables.
Rate ratios are not calculated where one or both of the rates have fewer than 5 young people in the numerator.
A reception occurs when a detention period starts and the young person:
To account for young people transported to court and returning to detention on remand or sentenced detention following a court hearing and for young people transferred between detention centres, the start of a detention period is considered a reception only when the detention period starts at least 2 full days after the end of the previous detention period.
A release from detention occurs where a detention period ends and the young person:
To account for young people transported to court and returning to detention on remand or sentenced detention following a court hearing and for young people transferred between detention centres, the end of a detention period is considered a release only when the detention periods ends at least 2 full days before the start of the next detention period.
All periods of sentenced supervision that start within one day of the end of a remand period are included except where there is a further remand period that starts on the same day as the period of sentenced supervision.
JJ NMDS reporting uses the Australian Standard Geographical Classification (ASGC) Remoteness Structure that the ABS has developed to analyse the remoteness of usual residence of the town or suburb of young people under supervision. This structure allows areas that share common characteristics of remoteness to be classified into broad geographical regions of Australia. These areas are Major cities, Inner regional, Outer regional, Remote, and Very remote.
In this classification, remoteness is determined based on the minimum road distance to differently sized urban centres, where the population size of the urban centre is assumed to determine the availability of goods and services.
Examples of places that are considered Major cities in the ASGC classification include Canberra and Newcastle. Hobart and Bendigo are Inner regional areas and Mackay and Darwin are Outer regional areas. Alice Springs and Mount Isa are Remote areas and Tennant Creek and Meekatharra are Very remote.
The remoteness of the young person's usual residence was determined using the most recent postcode of their last known address. Young people with invalid, missing or unknown postcodes of last known home address were excluded from the analysis.
The number of young people under supervision in each remoteness area was estimated based on each young person's most recent postcode. Some postcode areas were split between two or more remoteness areas. Where this was the case, the data were weighted according to the proportion of the population of the postcode area in each remoteness area. Some young people may appear in remoteness areas for which there is no population within that state or territory. This is due to young people whose last known home address is in a different state or territory to the one in which they are under supervision.
JJ NMDS reporting uses the Socio-Economic Indexes for Areas (SEIFA) that the ABS has developed to analyse the socioeconomic position of the usual residence of young people under supervision.
The SEIFA comprises four indexes that are constructed using information from the five-yearly Census of Population and Housing. These four indexes are the Index of Relative Socio-Economic Disadvantage, the Index of Relative Socio-Economic Advantage and Disadvantage, the Index of Economic Resources and the Index of Education and Occupation.
The Index of Relative Socio-Economic Advantage and Disadvantage is used to compare the average level of socioeconomic advantage and disadvantage in the areas of usual residence of those under supervision. The Index of Relative Socio-Economic Advantage and Disadvantage is derived from census variables related to both advantage and disadvantage, including low levels of income and education, as well as high levels of education and income. This index can be used to measure both disadvantage and advantage. A high score indicates a relatively high level of advantage and a relatively low level of disadvantage. An area containing some relatively disadvantaged people and some relatively advantaged people may have a low score on the Index of Relative Socio-economic Disadvantage, due to the levels of disadvantage, but a relatively high score on the Index of Relative Socio-economic Advantage and Disadvantage, due to the existence of both advantage and disadvantage. Population-based quintiles are used.
The socioeconomic position of the area of the young person's usual residence was determined by allocating the relevant SEIFA population-based (2011 population) quintile score to the most recent postcode of the last known home address. Young people with invalid, missing or unknown postcodes of last known home address were excluded from the analysis.
The number of young people under supervision in each area was estimated based on each young person's most recent postcode. Some postcode areas were split between two or more areas with different SEIFA scores. Where this was the case, the data were weighted according to the proportion of the population of the postcode area in each SEIFA area.
The SEIFA represents the average of all people living in the area, and not the socioeconomic position of a particular individual living in the area. Therefore, socioeconomic analyses in JJ NMDS reporting indicate the level of socioeconomic advantage and disadvantage in the area of usual residence of the young person, not the level of socioeconomic advantage and disadvantage of the young person or their family. Some young people may appear in socioeconomic areas for which there is no population within that state or territory. This is due to young people whose last known home address is in a different state or territory to the one in which they are under supervision.
A supervision period is the period of time a young person spent under continuous youth justice supervision. It should be noted that:
Young people may not serve the full duration of orders for several reasons, including:
An example of the relationship between periods, episodes and orders is shown in the figure below. In this example, a young person spent 6 continuous months under supervision, with the first 2 months under community-based supervision and the remaining 4 months in detention. The young person experienced two different types of community supervision in the first 2 months (e.g. probation and bail). The young person then experienced two different types of detention (e.g. remand and sentenced detention).
The JJ NMDS contains information on the type of supervision using the national classification of supervised legal arrangements and orders.
In JJ NMDS reporting, several of these order types are routinely combined, including other orders not elsewhere classified, probation and similar orders, supervised or conditional bail and other unsentenced community-based orders, and unsentenced detention.
Other orders not elsewhere classified are classified as 'other' in tables disaggregated by legal status.
'Probation and similar' is composed of these order types with additional mandated requirements and those without additional mandated requirements. Young people who are supervised under both types of order on the same day or during the same year are counted only once for this category.
This category includes young people on supervised or conditional bail, home detention bail and other unsentenced community-based supervised orders. Young people who are supervised under more than one of these types of orders on the same day or during the same year are counted only once for this category.
This category includes young people in police-referred detention and on court-referred remand. Young people who are detained for both these types of detention on the same day or during the same year are counted only once for this category.
Where the number of young people under supervision on an average day is relatively small, the amount of random variation from year to year is more noticeable. This may affect the appearance of trends, which should therefore be interpreted with caution, particularly where they relate to small numbers. In recognition of this, percentage changes are not calculated where they relate to groups of fewer than 100 people.
Youth justice in Australia reports aim to highlight the overall or net change over a defined period (that is, comparing the start and end of the period), while taking into account the trend within the period.
Trend data may differ from data published in previous versions of Youth justice in Australia (previously Juvenile justice in Australia) due to data revisions.
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