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Research Using Administrative Data to Support the Work of the Expert Panel on Modernising Child, Youth and Family

Appendix 1: Study population and definitions

The study uses data from Statistics New Zealand's Integrated Data Infrastructure (IDI), which combines and integrates administrative data from a range of government agencies, including Inland Revenue, the Ministry of Education, the Ministry of Health, the Ministry of Social Development and the Department of Internal Affairs.[1]

The full IDI population of identities is an ‘ever in NZ' population covering any NZ born individual, anyone granted a permanent residency visa since 1998 and any one ever registered with the IRD. Depending on the research objectives this ‘super-population' generally needs to be filtered to remove people not in NZ for very long, people who left NZ a long time ago.

The 1993 cohort population used to produce the “life charts” in this study comprises New Zealanders who were born in 1993 and satisfied the conditions listed in Table 1.

Appendix Table 1 - Study population criteria
  Selection criteria
1 Born in 1993
2 Enrolled as domestic students in New Zealand schools in 2008 or 2009 (ie, when they were aged 15 and 16 years
3 Living in NZ for most (6 months or more) of their 20th year
4 Link to an identity on the IDI ‘spine' (this means they have an IRD number or are NZ born or were granted a permanent residency visa)

There are 56,300 individuals satisfying these conditions in the IDI.

Defining the 1993 cohort population in this way means that we exclude those for whom we have insufficient evidence to determine whether they are “on track”. This means:

  • We do not include New Zealand resident individuals born in 1993 who had left New Zealand before their secondary schooling years.
  • We do not include individuals born in 1993 who attended secondary school in NZ but who subsequently have emigrated.
  • We do include non-NZ born individuals who went to secondary school in NZ (as domestic students in 2008 or 2009) and who appear to be still in NZ at age 21.

Table 2 describes the various characteristics and life events used to describe the interactions the different groups of children in the cohort have had with government agencies throughout their childhood.

Appendix Table 2 - Characteristics and life events - notes on definitions
Characteristic Notes: Number in 1993 Cohort Prevalence in 1993 Cohort
Older sibling had CYF notification prior to child's birth For this analysis only siblings that are present in welfare data are included 1,098 1.9%
Caregiver had served corrections sentence prior to child's birth Only caregivers identified through the welfare data are included (it is not until 1998 data that birth parents are fully identified in IDI data) 4,863 8.6%
Family was supported by welfare at child's birth   11,571 20.5%
Child had CYF notification prior to age 5 Note that CYF data lacks completeness pre-2000 so affects the early age data for this cohort 4,467 7.9%
Caregiver with corrections sentence whilst child less than 5 Corrections sentences include community or custodial sentences 6,720 11.9%
Family supported by welfare whilst child less than 5 This refers to where family was supported more than 25% of the days child was less than 5 17,637 31.3%
Child spent at least 1 night in hospital aged less than 5   15,081 26.8%
Child had CYF notification whilst aged 5 to 12 Note that CYF data lacks completeness pre-2000 so affects the early age data for this cohort 6,078 10.8%
Caregiver with corrections sentence whilst child aged 5 to 12   5,316 9.4%
Family supported by welfare whilst child aged 5 to 12 This refers to where family was supported more than 25% of the days child was between 5 and 12 16,473 29.3%
Child spent at least 1 night in hospitalwhilst  aged 5 to 12   10,680 19.0%
Child had CYF notification whilst aged 13 to 17   6,942 12.3%
Caregiver with corrections sentence whilst child aged 13 to 17   4,110 7.3%
Family supported by welfare whilst child aged 13 to 17 This refers to where family was supported more than 25% of the days child was between 13 and 17 10,524 18.7%
Child spent at least 1 night in hospital aged 13 to 17   9,084 16.1%
Changed high school at least once   16,530 29.4%
Left school before turning 18   28,359 50.4%
Truant, suspended or stood down from school   12,537 22.3%
Did not achieve NCEA level 2 equivalent   14,337 25.5%
Referred to CYF Youth Justice services Note: this indicator refers only to CYF Youth Justice services 2,571 4.6%
Parent before aged 20   4,161 7.4%
Used drug or alcohol addiction services before 20 Mental health service use data complete only up to 2012 when this analysis completed 1,680 3.0%
Served Corrections sentence before age 21 This refers to community sentences served as an adult 3,555 6.3%
Served custodial sentence before aged 21 This refers to custodial sentences served as an adult 1,005 1.8%
Received welfare benefit for more than 2 years before 21 This refers to main welfare benefits received as an adult 4,026 7.1%
  (these indicators were derived for use in the main report: He Tirohanga Mokopuna (the Statement of the Long Term Fiscal Position 2016):  
Child ever had CYF notification 11,538 20.5%
Family supported by welfare 25% of time aged 0-4 or 5-12 or 13-17 22,485 39.9%
Child spent at least 1 night in hospital whilst  aged 0-17 26,046 46.3%
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