Quality notes, issues and corrections

In line with Census Office’s revisions and corrections policy, thorough quality checks will take place on all census statistics which are released. Census Office may occasionally need to revise statistics and update information.

Details of where Census Office have discovered an issue with or correction to Census 2021 data are contained in the log for easy reference.

This page also contains a number of quality notes to help users understand quality considerations of the data.

DI003: Ever worked

Type: Issue

Date added: 31 May 2023

Comment

Individual question 33 on the 2021 Census questionnaire is only asked of individuals (aged 16 or over) who indicated that they were not working in the week prior to the census.  It asks ‘Have you ever done any paid work?’ with tick box options given for recording a response. 

The wording of the ‘Ever worked’ question was updated from the 2011 Census where it asked ‘Have you ever worked?’ and if yes, asked for the respondent to record the year last worked.  The response to this ‘Ever worked’ question is used in the ‘Employment History’ and ‘National Statistics Socio-economic Classification’ (NS-SeC) census outputs.

The percentage of the population aged 16 or over with a ‘No – Never worked’ response to this question increased from 10.3% (147,000) in Census 2011 to 13.4% (203,000) in Census 2021.  This appeared high when put in the context of a growing labour market.

In addition, the results of the Census Quality Survey (CQS) for this question showed a low agreement rate of 52.9% (all other questions produced agreement rates that were above 70%), indicating that there could be an issue with question understanding.  More detail on the CQS and the agreement rates for other Census 2021 questions can be found in the CQS information paper

To examine the ‘Ever worked’ response further, comparisons were made to a similar question in Labour Force Survey (LFS). The percentages of the population aged 16 to 64 with a ‘Never had paid employment’ response to the LFS (January to March) in 2021 and 2022 were 12.4% (144,000) and (152,000) 13.0%. When the Census 2021 ‘No – Never worked’ responses are limited to those aged 16 to 64 the equivalent percentage is 12.3% (146,000).  Therefore, the Census 2021 ‘Ever worked’ results are broadly consistent with LFS results from a similar question.  More detail on the LFS and additional years for ‘Never had paid employment’ results are available to download as a table on the NISRA website (Excel 25.6KB).

However, where individuals with a ‘No – Never worked’ response in Census 2021 could be linked to previous census responses, it showed that around 55,000 of the 203,000 that responded ‘No – Never worked’ in Census 2021 had previously given information stating that they were either working or had previously worked.  So while the Census 2021 responses are similar to LFS, there is still some evidence to suggest an issue.

This needs further, more detailed investigation but rather than withhold the variables from Census 2021 releases, the data has been published and accompanied by this issue note.

QN005: Economic activity related statistics

Type: Quality note

Date added: 21 March 2023

Comment

The coronavirus (COVID-19) pandemic will have affected the local labour market. This will have impacted on responses to the labour market questions on the census. For example, it is possible that some people on furlough may have identified as economically inactive, instead of temporarily away from work.

Users should be aware of this when using these and other labour market statistics

QN004: Migration related statistics

Type: Quality note

Date added: 21 March 2023

Comment

It is important to note that migration related statistics from Census 2021 will have been impacted by the travel restrictions put in place as a result of the coronavirus (COVID-19) pandemic. It has not been possible to quantify the effects of such restrictions, but the statistics are still considered useful in the context of measuring migration patterns between March 2020 and March 2021.

QN003: Marital and civil partnership status, and household relationships

Type: Quality note

Date added: 21 March 2023

Comment

The census responses contained larger than expected numbers of individuals reporting to be in a civil partnership. Information from the relationship question on the census questionnaire suggested that some of these individual marital and civil partnership status question responses were erroneous.

Census Office used this relationship information to amend a small number of marital and civil partnership status question responses where an inconsistency was clearly identified. This was only possible where people lived with their partner in the same household.

Therefore, only combined estimates for the marital and civil partnership status for the groups ‘Separated (but still legally married or still legally in a civil partnership)’, ‘Divorced or formerly in a civil partnership which is now legally dissolved’, and ‘Widowed or surviving partner from a civil partnership’ are available.

Alongside this, the complexity of ‘within household’ living arrangements may mean that household relationship statistics do not match individual level marital and civil partnership status statistics in all cases.

Users should be aware of this when using these and other statistics from these two outputs.

QN002: Place of study

Type: Quality note

Date added: 21 March 2023

Comment

Census Office identified an apparent issue, where some schoolchildren or students in full-time education had missing places of study. An exercise was carried out with educational administrative data to, where possible, identify the educational institution attended.

For those records where the educational institution attended could be identified, the census record was updated with the name, address, and associated location variables to enable distance travelled to place of study to be calculated.

QN001: Sexual orientation

Type: Quality note

Date added: 21 March 2023

Comment

The question on sexual orientation was asked of people aged 16 and over and was new for Census 2021. The law underpinning the census makes it a duty for respondents to complete their questionnaire, however, the question on sexual orientation has no statutory penalty.

In general, a process called item imputation was used to model missing census responses for other questions – however, this was not applied to the sexual orientation question. Therefore, the statistics published in ‘MS-C01 Sexual orientation’ includes the number of people who did not state their sexual orientation under the label ‘Not stated’ (3.3% in total for Northern Ireland).

DI002: Accommodation type

Type: Issue

Date added: 15 December 2022

Comment

Household question 7 on the 2021 Census questionnaire asks ‘What type of accommodation is this?’ with tick box options given for recording a response.

Census Office has noted differences in classification declared by a small number of respondents for accommodation type when compared to the accommodation type recorded by Land and Property Services (LPS) for the address. This can be explained by census respondents favouring selecting ‘semi-detached’ instead of ‘terraced (including end-terrace)’ for end-terrace properties.

It is consistent with previously published Office for National Statistics (ONS) research comparing responses to the 2011 Census question ‘What type of accommodation is this?’ with data trained surveyors have reported to the Valuation Office Agency (VOA).  The ONS research identified a preference for 2011 Census respondents to define their property as ‘semi-detached’ instead of ‘end-terrace’ in approx. 3% of cases.

This issue is related to the classification selected by respondents and does not affect the total number of properties recorded.

DI001: Rounding difference between census data published in May 2022 and September 2022

Type: Issue

Date added: 22 September 2022

Comment

The main statistics demography tables that form part of the ‘Census 2021 main statistics for Northern Ireland (phase 1)’ release supersede the population and household estimates published in the 24 May 2022 release, which reported statistics solely at the Northern Ireland level.

In May 2022, NISRA published rounded Northern Ireland level population and household estimates. At that time, the dataset was still being subjected to a number of final statistical procedures; these statistical procedures have been applied to the census database, and the unrounded statistics are now available. A number of figures at the Northern Ireland level (when rounded to the nearest 100) differ from the May figures as detailed in Table 1 and 2.