Quality Statement

Label
Sex at birth - 2023 Census: Information by concept en-NZ
Preface

The 2023 Census implemented the Data standard for gender, sex, and variations of sex characteristics. Sex at birth and gender data are collected together to derive cisgender and transgender status.

It is recommend viewing this sex at birth information by concept alongside the information by concepts for gender, cisgender and transgender status, and variations of sex characteristics for important context about how these concepts interrelate and the recommended use of data.

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Definition

Sex at birth refers to the sex recorded at a person’s birth (for example, what was recorded on their birth certificate). Sex at birth may also be understood as sex assigned at birth.

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Overall quality rating

Very high quality
Data quality processes section below has more detail on the rating.

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Priority level

Priority level 1

A priority level is assigned to all census concepts: priority 1, 2, or 3 (with 1 being highest and 3 being the lowest priority).
Sex at birth is a priority 1 concept. Priority 1 concepts are core census concepts that have the highest priority in terms of quality, time, and resources across all phases of a census.

Sex at birth is a new concept in the 2023 Census. It replaces sex, which was a priority 1 variable.

The 2023 Census: Final content report has more information on priority ratings for census concepts.

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Subject population

Census usually resident population count
This question applies to all people in New Zealand on census night. However, sex at birth data is usually output for the census usually resident subject population.
‘Subject population’ means the people, families, households, or dwellings that the variable applies to.

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How this data is classified

Sex at birth is classified into the following categories:

Census Sex at Birth Output V1.0.0 – level 1 of 2

Code Category
11 Male/Tāne
22 Female/Wahine
99 Not elsewhere included

Sex at birth uses a 2-level hierarchical classification. Level 1 categories are presented in the table above.

The level 1 residual category ‘Not elsewhere included’ contains the level 2 residual categories of ‘Response unidentifiable’ and ‘Not stated’. Follow the link above the table to examine the classification in more detail.

This classification is different from that used for sex in the 2018 Census.

Standards and classifications has information on what classifications are, how they are reviewed, where they are stored, and how to provide feedback on them.

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Question format

Sex at birth data is collected from the individual form (question 4 paper form). The question asked ‘What was your sex at birth?’ and included response options of ‘male’ and ‘female’. The question also contained guidance: ‘For example, what was recorded on your birth certificate’.

In the 2018 Census, the question on the forms read ‘Are you?’, with ‘male’ and ‘female’ as the response options. While data collected from this question was output as ‘sex’, the question was not labelled as such on forms and was open to respondent interpretation as to whether sex or gender was being asked.

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

On the online form:

  • sex at birth could only be answered with a single response
  • a response to either gender or sex at birth was required to continue filling in the census form and for the form to be submitted.

On the paper form:

  • non-response and multiple responses were possible.

Data from the online forms may therefore be of higher overall quality than data from paper forms. However, processing checks and edits were in place to improve the quality of the paper form data.

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

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Examples of how this data is used

Data-use outside Stats NZ:

  • by the health sector to understand populations for certain screening services, for example, cervical screening.

Data-use by Stats NZ:

  • used in combination with gender to derive cisgender and transgender status
  • used to provide a base population for fertility-derived series
  • used to produce population estimates and projections.
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Data sources

Alternative data sources were used for missing census responses and responses that could not be classified or did not provide the type of information asked for. The table below shows the distribution of data sources for sex at birth data.

Data sources for sex at birth data, as a percentage of census usually resident population count, 2023 Census
Source of sex at birth data Percent
2023 Census response 85.9
Historical census 2.1
 2018 Census 1.7
 2013 Census 0.4
Admin data 11.3
Deterministic derivation 0.0
Statistical imputation 0.6
 CANCEIS(1) donor's response sourced from 2023 Census form 0.6
 CANCEIS donor's response sourced from 2018 Census <0.1
 CANCEIS donor's response sourced from 2013 Census <0.1
 CANCEIS donor's response sourced from admin data <0.1
No information 0.0
Total 100.0
1. CANCEIS = imputation based on CANadian Census Edit and Imputation System

Note: Due to rounding, individual figures may not always sum to the stated total(s) or score contributions.


Admin data was sourced from the Department of Internal Affairs to replace missing or residual responses. If this was not available, historical census data from the 2013 and 2018 Censuses was used, followed by information from a derived Integrated Data Infrastructure table (containing information from a range of admin data sources and representing a mixed sex/gender concept). Statistical imputation was used for the remaining missing values.

Methodologies for filling gaps in gender and sex at birth concepts for the 2023 Census provides more detailed explanations about the methodology.

Editing, data sources, and imputation in the 2023 Census describes how data quality is improved by editing and how missing and residual responses are filled with alternative data sources (admin data and historical census responses) or statistical imputation. The paper also describes the use of CANCEIS (the CANadian Census Editing and Imputation System) which is used to perform imputation. This webpage also contains a spreadsheet that provides additional detail on the admin data sources.

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Missing and residual responses

Missing and residual responses represent data gaps where respondents either did not provide answers (missing responses) or provided answers that were not valid (residual responses).

Sex at birth data contains no missing or residual responses as they were filled with data from alternative sources.

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Data quality processes

Overall quality rating: Very high
Data is being 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
  • accuracy of response.

The lowest rated metric determines the overall quality rating.

Data quality assurance in the 2023 Census provides more information on the quality rating scale.

Data sources and coverage: Very high quality
The quality of all the data sources that contribute to the output for the variable were assessed. To calculate the data sources and coverage quality score for a variable, each data source was rated and multiplied by the proportion it contributes to the total output.

The rating for a valid census response is defined as 1.00. Ratings for other sources are the best estimates available of their quality relative to a census response. Each source that contributes to the output for that variable is then multiplied by the proportion it contributes to the total output. 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 high proportion of sex at birth data received from 2023 Census forms, alongside the high quality of alternative data sources, resulted in a score of 1.00 – a quality rating of very high.

Data sources and coverage rating calculation for sex at birth data, census usually resident population count, 2023 Census
Source of sex at birth data Rating Percent Score contribution
2023 Census response 1.00 85.88 0.86
2018 Census 1.00 1.73 0.02
2013 Census 0.98 0.42 <0.01
Admin data 1.00 11.33 0.11
CANCEIS(1)nearest neighbour imputation 0.90 0.64 0.01
No information 0.00 0.00 0.00
Total 100.00 1.00
1. CANCEIS = imputation based on CANadian Census Edit and Imputation System
Note: Due to rounding, individual figures may not always sum to stated total(s) or score contributions.

Consistency and coherence: Very high quality
The sex at birth data is highly consistent with expectations across all consistency checks.

Where there are changes in the trend to the male/female distribution, these align with understanding of ongoing population trends and understanding of the 2023 Census collection and methodology (slightly higher levels of migration of males and possible improvements in coverage).

The impact of the concept refinement from sex to sex at birth is unlikely to have impacted this distribution in an observable manner, as the proportion of those with gender different to their sex at birth (who may have answered the 2018 question according to a gender/current sex understanding) is relatively evenly distributed across males and females by sex at birth, and in small numbers overall.

Accuracy of responses: Very high quality
Sex at birth data has no accuracy of response issues that have an observable effect on the data. The quality of coding is very high. Any issues with the variable appear in a very low number of cases (typically less than a hundred).

Improvement in scanning repair for paper forms reduced the number of responses needing to be sourced from alternative sources.

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Recommendations for use and further information

Where sex at birth information is used, it is appropriate for use at low levels of geography and cross-tabulation with other census data. Stats NZ recommends use of the gender concept as the primary demographic variable to distinguish between males, females, and other genders. Stats NZ recommends the use of sex at birth information specifically when there is a need to analyse data in relation to the sex at birth concept. Analysis of differences between the 'gender' and 'sex at birth' concepts should be done through the ‘Cisgender and transgender status’ variable.

Comparisons to other data sources

  • Stats NZ will produce some census products with sex at birth information that use the 2013 and 2018 sex data as a time series comparison. While this data is highly comparable, users should note the revision in concept between 2018 and 2023. The information collected in 2018 and prior was not specifically sex at birth.
  • Census aims to be a national count of all individuals in a population while other surveys (such as the Household and Labour Force Survey and the General Social Survey) measuring this variable are only based on a sample of the population.

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Information by variables from previous censuses

Sex at birth is a new concept in the 2023 Census. It replaces sex, which has been used for time series data. To see how the sex at birth concept aligns with the sex variables from the previous censuses, use the links:

Contact our Information centre for further information about using this concept.

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Information

History

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Revision Date Responsibility Rationale
57 26/09/2024 10:00:58 AM