Variable Description

Iwi (information about this variable and its quality)
Iwi (information about this variable and its quality)

An iwi, or Māori tribe, is one of the largest kinship groupings and is generally made up of several hapū that are all descended from a common ancestor. Hapū are clusters of whānau where the whānau is usually an extended family grouping consisting of children, parents, often grandparents, and other closely related kin.

For statistical purposes, an iwi is defined as a whakapapa-based kinship grouping that generally has several hapū and one or more active marae, and a recognised structure that represents the interests of the iwi, such as a rōpū whakahaere, committee, or board.

Other Variable Information

Stats NZ will not release official statistical counts of iwi from the 2018 Census. This is because of the very poor-quality data, primarily due to the level of missing iwi affiliation data, and the absence of alternative data sources for where there is no information.

In June 2021, ongoing work completed in collaboration with iwi technicians from the Data Iwi Leaders group (Data ILG), enabled the release of iwi affiliation estimates. While these estimates are not official 2018 Census counts, for many purposes these estimates provide improved accuracy and relevance for iwi than continued use of 2013 Census iwi counts. 2018 Iwi Affiliation Estimated Counts – DataInfo+ provides more information on the quality of this dataset.

The purpose of this Information by Variable is to provide detail on the information we collected, the questionnaire design and further commentary on the reasons why the 2018 Census iwi affiliation counts were evaluated as very poor quality and subsequently not released.

Priority level

Priority level 2

We assign a priority level to all census variables: Priority 1, 2, or 3 (with 1 being highest and 3 being the lowest priority).

Iwi affiliation is a 2018 Census priority 2 variable. Priority 2 variables cover key subject populations that are important for policy development, evaluation, or monitoring. These variables are given second priority in terms of quality, time, and resources across all phases of a census.

The census priority level for Iwi affiliation remains the same as the 2013 Census.

Quality Management Strategy and the Information by variable for Iwi (2013) have more information on the priority rating.

Overall quality rating for 2018 Census

Very poor quality

Data quality processes section below has more detail on the rating for this variable.

The External Data Quality Panel has commented on the quality of this variable. Initial Report of the 2018 Census External Data Quality Panel has more information.

The 2018 iwi affiliation estimated counts are rated as moderate to poor quality. 2018 Iwi Affiliation Estimated Counts – DataInfo+ provides more information on the quality of this dataset.

Subject population

Māori descent census usually resident population

‘Subject population’ means the people, families, households, or dwellings to whom the variable applies.

Iwi affiliation data is also collected where provided for respondents who selected ‘don’t know’ to the Māori descent question but provide an iwi affiliation. However, these respondents are not included in the subject population for the Iwi affiliation variable.

How this data is classified

Iwi 2 V2.0.0

Iwi affiliation is a hierarchical classification with three levels. Level 1 contains 17 categories with iwi coded by region (01-11), Confederations and Waka (20), and Hapū affiliated to more than one iwi (22). These categories are:

01 Te Tai Tokerau/Tāmaki-makaurau (Northland/Auckland) Region Iwi

02 Hauraki (Coromandel) Region Iwi

03 Waikato/Te Rohe Pōtae (Waikato/King Country) Region Iwi

04 Te Arawa/Taupō (Rotorua/Taupō) Region Iwi

05 Tauranga Moana/Mātaatua (Bay of Plenty) Region Iwi

06 Te Tai Rāwhiti (East Coast) Region Iwi

07 Te Matau-a-Māui/Wairarapa (Hawke's Bay/Wairarapa) Region Iwi

08 Taranaki Region Iwi

09 Whanganui/Rangitīkei (Wanganui/Rangitīkei) Region Iwi

10 Manawatū/Horowhenua/Te Whanganui-a-Tara (Manawatū/Horowhenua/Wellington) Region Iwi

11 Te Waipounamu/Wharekauri (South Island/Chatham Islands) Region Iwi

20 Confederations and Waka, iwi not named

21 Iwi named, region not known

22 Hapū affiliated to more than one iwi

23 Region known, iwi not named

44 Don't Know

99 Not elsewhere included

Level 3 contains 180 iwi and iwi-related categories. ‘Not elsewhere included’ contains the residual categories of ‘refused to answer’, ‘response unidentifiable’, ‘response outside scope’ and ‘not stated’.

Up to five categories can be selected. Therefore, the number of total responses will be greater than the number of respondents. However, Iwi affiliation can be classified according to the number of iwi specified.

Although there have been no conceptual changes to this variable, 36 new categories were added to the classification since the 2013 Census, which used the previous Iwi New Zealand Standard Classification V6.0.

Our website provides more information on the revised iwi statistical standard.

Question format

Iwi affiliation comes from the name(s) and region(s) of iwi affiliations on the individual form (question 13 on the paper form). Iwi indicator (question 12 on the paper form) is the preliminary question on the individual form.

Stats NZ Store House has samples for both the individual and dwelling paper forms.

There were changes in the question format since the 2013 Census:

  • in 2018, there were separate questions for the Iwi indicator and the name(s) and region(s) of iwi. In 2013, these were asked in the same question on the paper form
  • in 2018, both iwi questions were on the front page of the paper form, following the Māori descent question. In 2013 the iwi question (number 15), was on page 2 of the paper form
  • in 2018, for the English language version of the iwi question, only the ‘names and region(s) of your iwi (tribe or tribe(s))’ was asked for whereas in 2013, respondents were asked to ‘print the name and home area, rohe or region of your iwi’.

There were also differences in the way a person could respond between the modes of collection (the online and paper forms).

On the online form:

  • respondents had to answer ‘yes’ to the Iwi indicator question in order for the name(s) and region(s) of iwi text fields to appear
  • only one name and one rohe/region textbox were initially displayed, but a respondent could click ‘add’ to provide up to five names and five rohe (for the te reo Māori version) or five regions (for the English language version)
  • as-you-type functionality helped respondents provide valid, detailed responses.

On the paper form:

  • it was possible for a person to only respond to the name(s) and region(s) of iwi without responding to the iwi indicator question
  • there was only space for four names and rohe/regions text boxes on the English paper form
  • for the bilingual form (as with all questions), te reo Māori and English versions of the iwi question were side by side on the same page, with one shared space to respond in either language. On the te reo Māori side, respondents were able to provide four iwi and rohe, and on the English side, respondents were able to provide four iwi and regions.

How this data is used

Outside Stats NZ

  • Monitor the performance of Treaty of Waitangi obligations by the Crown and iwi.
  • Help the allocation of resources and funds to iwi.
  • Help with Waitangi Tribunal decisions on, for example, land ownership and fishing rights.
  • Help in iwi planning and social and economic development.
  • Help central, regional, and local government agencies, as well as a range of NGOs, researchers and iwi organisations to evaluate, monitor, plan and provide services to iwi in areas such as housing, health, social welfare, and special assistance programmes.
  • Help local government in administrating the Resource Management Act 1991.

2018 data sources

No alternative data sources or imputation were available to replace missing responses or responses that could not be classified for the Iwi affiliation variable.

2018 Iwi affiliation – Māori descent census usually resident population
Source Percent
Response from 2018 Census 71.3 percent
2013 Census data 0.0 percent
Administrative data 0.0 percent
Statistical imputation 0.0 percent
No information 28.7 percent
Total 100 percent
Due to rounding, individual figures may not always sum to the stated total(s)

The ‘no information’ percentage is where we were not able to source iwi data for a person in the subject population.

Missing and residual responses

No information’ in the data sources table, is the percentage of the subject population coded to ‘not stated’.

The 2018 Census had a lower than expected response rate. This particularly impacted the Iwi affiliation variable where over 20 percent of the Māori descent population were enumerated from admin sources and, at the time, it was not possible to obtain iwi affiliation data for them.

The ‘not stated’ percentage is substantially higher than in the 2013 Census because the admin enumerated records in the Māori descent population are included in the subject population for Iwi affiliation. In 2013, substitute records (created when we had evidence that a person existed within a dwelling but did not have a census response) were excluded from the Iwi affiliation subject population because the Māori descent variable was previously not imputed.

Additionally, non-response was evident on received forms:

  • it was possible to not respond to the iwi question even when respondents were directed to it from the Māori descent question
  • some respondents of Māori descent indicated they knew their iwi but did not provide their iwi affiliation(s).

Percentage of ‘not stated’ for the Māori descent census usually resident population:

  • 2018: 28.7 percent
  • 2013: 3.1 percent
  • 2006: 4.3 percent.

Responses that could not be classified or did not provide the type of information asked for such as ‘response outside of scope’ and ‘response unidentifiable remain in the 2018 Census counts and are included in the ‘Response from 2018 Census’ percentage in the data sources table above.

The residual category responses are also grouped together with ‘not stated’ for the ‘not elsewhere included’ category:

Percentage of ‘not elsewhere included’ for the Māori descent census usually resident population:

  • 2018: 29.3 percent
  • 2013: 3.3 percent
  • 2006: 4.3 percent.

2013 Census data user guide provides more information about non-response in the 2013 Census.

Data quality processes

Overall quality rating: Very poor quality

Data was evaluated to assess whether it meets quality standards and is suitable for use.

Three quality metrics contributed to the overall quality rating:

  • data sources and coverage
  • consistency and coherence
  • data quality.

The lowest rated metric determines the overall quality rating.

Data quality assurance for 2018 Census provides more information on the quality rating scale.

Data sources and coverage: Very poor quality

We have assessed the quality of all the data sources that contribute to the output for the variable. As no alternative data sources or imputation were used to replace missing responses, the final data sources and coverage quality rating for Iwi affiliation reflects the lower than expected response to the census overall and the high proportion of admin enumerated records for those respondents of Māori descent.

The rating for a valid census response is defined as 1.00. This is then multiplied by the overall proportion of responses from 2018 Census forms. The total score then determines the metric rating according to the following range:

  • 98–100 = very high
  • 95–<98 = high
  • 90–<95 = moderate
  • 75–<90 = poor
  • <75 = very poor.

The low proportion of data from received forms therefore contributed to the score of 0.71, determining the very poor rating.

Quality rating calculation table for the sources of Iwi affiliation – 2018 Māori descent census usually resident population
Source Rating Percent of total Score contribution
2018 Census form 1.00 71.31 0.71
No Information 0.00 28.69 0.00
Total 100.00 0.71
Due to rounding, individual figures may not always sum to the stated total(s) or score contributions.

It was decided, at the time, not to use 2013 Census data to fill the gaps as it would not capture changes in affiliation for individuals over time and could not be guaranteed as an accurate predictor of present iwi affiliation. The significant change in the classification also inhibited the use of 2013 data.

For the iwi affiliation estimated counts, the use of 2013 Census iwi affiliation responses was re-assessed under Data ILG’s guidance. Methodology for the 2018 iwi affiliation estimated counts provides more information on the use of 2013 data in the iwi affiliation estimated count dataset.

Consistency and coherence: Poor quality

Iwi affiliation data is not consistent overall with expectations across one or more consistency checks. There is an overall difference in the data compared with expectations and benchmarks. Where this difference occurs, it cannot be fully explained through likely real-world change, incorporation of other sources of data, or a change in how the variable has been collected.

Due to the high non-response rate and changes to the classification, Iwi affiliation data is not comparable with the time series. In addition, fewer people answered the Iwi affiliation question with more than two iwi when answering the 2018 question online than in the 2013 Census. This was particularly evident for respondents who completed the 2013 Census on paper but completed the 2018 Census online.

The consistency checks for Iwi affiliation were carried out at the Territorial Authority Local Board (TALB) level of geography. Due to the high levels of non-response and admin enumeration of individuals in the Māori descent population, variability is more marked for certain regions at lower level geographies.

Data quality: Moderate quality

Iwi affiliation has various data quality issues involving several categories or aspects of the data, or an entire level of a hierarchical classification. The data quality issues include problems with the classification or coding of data, such as vague responses resulting in coding issues, or responses that cannot be coded to a specific (non-residual) category, thereby reducing the amount of useful, meaningful data available for analysis.

There were some improvements in data quality when compared with 2013. For example:

  • the use of the online form and the as-you-type list allowed for higher accuracy and a larger volume of auto-coding
  • there were improvements in iwi synonym coding.

Further information

Iwi affiliation data from the 2018 Census is not suitable for providing an official iwi count.

To reduce the impact of this missing data, Stats NZ and technicians of the Data Iwi Leaders Group have worked together to enable the release Iwi affiliation (estimated counts): 2018, published in June 2021. This provides iwi estimates with a select number of individual 2018 characteristics (for example, age and income). 2018 Iwi affiliation estimated counts – DataInfo+ provides detailed information on the quality of the 2018 Iwi Affiliation Estimated Counts dataset, and Strengths and limitations of 2018 iwi affiliation estimated counts provides high level guidance on using these estimates.

Contact our Information Centre for further queries relating to this variable.

This variable is not part of a dataset.


Aggregation Method