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]


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:

  1. Areas (meshblocks) selected first.
  2. Households (dwellings) within areas selected second.
  3. 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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