Northern Ireland Longitudinal Study (NILS)

Northern Ireland Longitudinal Study microdata are available resources for a variety of research studies

NILS 2021 is now available to access.  The NILS database has been updated with 2021 Census data extracts thus extending the research data coverage to 40 years and significantly enhancing the continued relevance and value of the NILS data for demographic, health and socio-economic research.

The NILS is proportionally the largest longitudinal study in the UK covering an impressive 28% of the Northern Ireland population and accounting for approximately 50% of Northern Ireland households. The NILS ‘core’ data are drawn from the Health Card Registration data and then linked to data from Census returns (1981, 1991, 2001, 2011 & 2021), Vital Events (births, deaths and marriages), Migration and Property data. The result is over 40 years of longitudinal data which is regularly being updated.

In addition to this rich resource there is the potential to link further Health and Social Care data via Distinct Linkage Projects. This includes Primary health care data (supplied by the Business Services Organisation) and secondary health care data available through the HSC Regional Data Warehouse (via the Honest Broker Service).  RSU will coordinate the signing of Data Access Agreements for the transfer of these data. 

NILS diagram


NIMS 2021 is now available to access.  For a more detailed investigation into NI mortality patterns the Northern Ireland Mortality Study (NIMS) contains links for the enumerated population of Northern Ireland from the 1991, 2001, 2011 and 2021 Censuses to registered mortality data from the General Register Office (GRO). Within this database, there are static Person and Household data sets for each Census link, as well as a linkage table to a Deaths information table.  

NIMS diagram

The NIMS 2011 was due to end in 2021 and it has now been extended to continue to include deaths data post 2021 linked to the enumerated population of Northen Ireland from the 2011 Census to allow for ongoing research into the impact of Covid on deaths in NI.  This will run alongside the newly released NIMS 2021 database which links the enumerated population of Northen Ireland from the 2021 Census to subsequent registered mortality data from GRO.  The NIMS databases are updated bi-annually, and both currently contain deaths up to June 2023. 

Vital Events blog - Suicide review 2022


The NILS and NIMS microdata are invaluable resources for a variety of research studies, focussing on a range of topics such as mental health, migration, commuting and working patterns. To find out more, please consult the NILS-RSU website or the NILS Annual Report.

Useful Documentation

Please consider the following policies and procedures documentation before continuing with your application: 

See the NILS/NIMS metadata and data dictionary (inclusive for NILS 2021) for information on the NILS/NIMS variables, sample structure, and sample membership

The NILS 2021 database was extensively tested before being released to the research community. During the first testing stage, the Alpha Test phase, a range of data quality checks were performed by RSU. 

Following the Alpha testing phase, the data was released to researchers for Beta testing. The objectives of the Beta testing phase were to test the NILS 2021 data for accuracy, comparability, and consistency through active analytical use. 

To apply for a NILS project click the link and follow the instructions: 

The NILS project modification form can be completed and submitted to RSU during the analysis phase if the research team identify the need for minor adjustments to timeframes, data, and research team members. This form can also be used to request the project be de-archived

All outputs (either intermediate or final) must be accompanied by an output form:

For information relating to confidentiality, please see the Code of Practice

Univariate Synthetic Data

NILS Univariate Synthetic data can now be requested to facilitate remote writing of code without needing access to the real data and the secure room.  Please note that timescales for producing the univariate synthetic data may vary according to resources and volume of requests.

Research Approvals Group

NILS projects will be considered by the Research Approvals Group (RAG), and are only approved when the following conditions are met:

  1. that there is a longitudinal aspect to the research;
  2. that the project relates to Health and Social Care research;
  3. that the project supports the development/delivery of public policy

For more details please see the NILS RAG criteria.

Dates of NILS RAG:

Application deadline: 23 May 2024 | NILS RAG: 6 June 2024

Please bear in mind that the application deadline is the date at which the final version of the application (following feedback from RSU) should be submitted to RSU. 

Time frame

NILS projects normally take 2 to 4 months from application submission to dataset creation. NILS DLPs can take six to eight months, with more complex linkages taking longer.

Ethics for NILS Projects

The NILS database has ethical approval from ORECNI (REC Reference Number 176/NI/0101).  However, if a potential project intends to link health data to the NILS database further ethical approval is required.  This ethical approval must be applied for by the research team. Further information can be obtained through the ORECNI website.

In applying for ethics, please note the following:

- RSU does not receive or process personal identifiable data. Each distinct linkage project requires encryption of the unique identification field (e.g. anonymised Health and Care Number).

- The use of an independent Trusted Third Party (TTP) team fulfils a vital role in ensuring the privacy of research subjects. RSU and TTP are managed and run separately to ensure that processes are independent.  TTP links the NILSIDs from the project sample to an anonymised representation of the Health and Care Number.

- The de-identified project-specific data is made available to the research team in the NISRA secure environment for analysis.