Sampling
This webpage looks at the sampling process used for the New Zealand Crime and Safety Survey (NZCASS).
More information can be found in the NZCASS Technical manual [PDF, 5.3 MB]
- Overview
- Multistage sampling
- Composition of sample
- Primary sampling unit (PSU)
- Number of PSUs selected
- Target population
- Sampled areas
- Areas excluded
- Dwellings included
- Dwellings excluded
- Eligible respondents
- Ineligible respondents
- Changes to sample design/process
Overview
The NZCASS is a nationwide, face-to-face random probability survey, with one respondent selected per household using multistage stratified cluster sampling methods.
Multistage sampling
The sample was drawn in a multistage sequence that started from an unstratified frame, through to clusters of dwellings, and then to a single respondent from each dwelling:
- Areas (meshblocks) selected first.
- Households (dwellings) within areas selected second.
- One respondent within each household selected third.
Final: Selection of a small number of incidents from those experienced by respondents.
Composition of sample
Two samples are drawn as part of the NZCASS: a general or 'main sample' and a Māori booster sample that aims to increase sample sizes for Māori.
Primary sampling unit (PSU)
Statistics New Zealand meshblocks (MBs).
Number of PSUs selected
1000 meshblocks were selected with probability proportional to size.
Target population
Total usually resident, non-institutionalised, civilian population of New Zealand aged 15 years and over.
Sampled areas
North Island, South Island and Waiheke Island.
Areas excluded
- Offshore islands other than Waiheke Island.
- PSUs containing fewer than nine dwellings were also excluded.
Dwellings included
Dwellings excluded
Eligible respondents
As noted above under ‘Target population’, eligible respondents were usually resident, non-institutionalised civilians aged 15 years and over.
To be eligible for the Māori booster sample, the respondent also had to identify as Māori.
Ineligible respondents
The following respondents were not eligible for the NZCASS:
- people who were present at the time of the interview but usually resided elsewhere (either within New Zealand or overseas)
- non-New Zealand diplomats and their non-New Zealand staff
- members of the non-New Zealand armed forces stationed in New Zealand
- overseas visitors who were in New Zealand for less than 12 months
- Children (15 years old and over) under shared custody arrangements if they spent more nights of the week elsewhere
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