Background

What is the NILS?

Why was the NILS set up?

What can the NILS be used for?

How does the NILS compare to other datasets?

How are the NILS data managed?

Is the NILS for me?

What is the NILS?

The Northern Ireland Longitudinal Study (NILS) is a large-scale data linkage study which has been created by linking administrative and statistical data.  The Study is designed for statistical and research uses only and is managed under Census legislation. Information is linked over time on people from Census, vital events and health registration datasets.  Data sources include 2001 Census data, birth and death registrations and demographic data derived from health registrations. More detail on the NILS data can be viewed by clicking on Data.

A Longitudinal Study has been successfully running in England and Wales since the 1971 Census. The England and Wales Longitudinal Study (LS) was designed as a sample around 500,000 people from the England and Wales population.  A similar study, the SLS, is also running in Scotland with a sample of nearly 300,000 people from the Scottish population.  

NILS members are selected on 104 annual birth dates. In total around 500,000 people are included in the Northern Ireland Longitudinal Study. The Study will be of interest to a wide variety of researchers.  Information on using the NILS is provided in this website.

In Northern Ireland it had been identified that there was an inability to link data held across Government at an individual level.  This is particularly important to monitor circumstances over a number of years to determine the success, failure or need for a particular policy.

The Department of Health and the Research and Development Office realised that an NI Longitudinal Study would have significant benefits in the development of research into the effectiveness of the Health Service in NI.  From this they agreed to jointly fund the setup of the NILS.

The NILS includes a range of variables which can be explored, including; cultural, demographic, economic, health, housing and social issues. Using the example of health, the potential uses of longitudinal studies such as the NILS are considerable.

Because of the inclusion of socio-demographic data from census and other sources an added dimension can be brought to the analysis of health variations and inequalities.

Social differentials in health and mortality can be explored using such measures as the Registrar General´s social class, deprivation indices, NSSEC, occupation and industry, housing tenure, car access, overcrowding and lack of amenities in housing, ethnicity and sex.

The effects of geography and migration can also be examined.

Change over time can be looked at with reference to a person´s later health or their cause of death because of the linkage of data from more than one census.

Events such as migration histories are also included. More information about the datasets that have been linked can be viewed in the Data section. More detailed information on all the variables held in the NILS can be found in the Data Dictionary section.

The England and Wales LS, which this dataset is modelled upon, has been used to look at a range of important questions including: occupational mortality, fertility changes, family reconstitution, women´s occupations, geographical and social inequalities in health, social mobility, ethnic health etc. Types of analyses include:

• Prospective analysis of census and event data. For example: studies of associations between employment status and mortality, between economic status and cancer registrations, or between socio-economic factors and fertility; survival analysis of mortality by area deprivation.
• Prospective analysis of successive event data. For example, studies of changes in birth spacing, associations between fertility and cancer survival.
• Cross-sectional analysis. especially for studies of ethnic or geographical factors.
• International comparisons. Countries such as France, Denmark, Finland and the USA have similar programmes to the LS and hence the NILS.

Much of the work done using this database in England and Wales has fed into government social policy, particularly into the health targets defined by the Department of Health. For further information about work conducted with the LS click on CeLSIUS Publications.

How does the NILS compare to other datasets?

In comparison to cross-sectional studies, longitudinal studies have many advantages.  With the ability to capture information of a sample at various time points, researchers can look at separating changes over time within individuals (aging effects) from differences among people in their baseline levels (cohort effects).  Other advantages include the ability to carry out survival analysis and longitudinal studies have shown an improvement in efficiency compared to other types of studies.

Previous longitudinal studies have a long history in British social and epidemiological research, with a majority of these being based on surveys or panel studies.  An example of one such survey is the British Household Panel Study (BHSPS) which has recently been extended to Northern Ireland.  The main objective of the BHSPS is to gain a further understanding of social and economic change at the individual and household level.  Information is gathered by interviewing members of sample households at various time points.

The NILS has been set up to collect data that is either required by law (Census, births and deaths registrations) or is a standard administrative function within the UK or Northern Ireland.  As a result, no additional burden is put on sample members.  In the England and Wales LS, it has been shown that the attrition rates are extremely low and linkage rates for events tend to be very high. Also, the sample size is very large compared to most surveys or panel studies.

How are the NILS data managed?

The NILS database is designed to provide ´safe data in a safe setting´. Much of the data held is confidential in nature and cannot be used in raw form. The database design has taken this into consideration and the NILS is not a publicly accessible dataset available through any of the academic data archives. It has been constructed as a data repository on a stand-alone network from which data can be accessed by dedicated staff. Further information on how to access the data can be viewed by selecting Access.

Is the Northern Ireland Longitudinal Study for me?

The NILS is useful for longitudinal and cross-sectional studies of census and event data.  It includes linked data on:

• Information from the 2001 Census which includes data on occupation, economic activity, housing, ethnicity, health, age, sex, marital status and education.
• Demographic data derived from health registrations.
• Event data on births and deaths, fertility, mortality, morbidity and migration.
• Geographical information.

The NILS can be used for a wide range of studies providing quality data for various kinds of analyses which other datasets cannot.  For more information on whether or not the NILS can contribute to your research contact the NILS team using the Contact Us link.