A variety of administrative and statistical data are linked in Northern Ireland Longitudinal Study (NILS) and Northern Ireland Mortality Study (NIMS) databases including: demographic and migration events data from the Northern Ireland Health Card Registration system, the 2001 Census returns and vital events registered with the General Register Office for Northern Ireland. For the NIMS resource, census returns of those enumerated in the 2001 Census are subsequently linked to death records only.
 
For detailed information on the NILS / NIMS databases please see the 'NILS Cohort Profile' and 'Introduction to the NILS'.

Full details of all the NILS/NIMS variables (including descriptions, field values and SPSS/STATA analysis code) are available in the NILS Data Dictionary.

A summary of the key dataset tables available to researchers are as follows:

NILS Core Datasets

Northern Ireland Health Card Registration system datasets are used to provide for core information for NILS sample members:

• CoreNILSData_Basic: basic record for all NILS members and variables include information on gender, location and date they joined the sample
• CoreNILSData_AddressHistory: information on all NILS member's addresses
• CoreNILSData_MigrationEvents: information on all NILS member's migration events
• CoreNILSData_XAGES: NILS member's age (restricted access)

2001 Census Datasets

NILS members are linked to the 2001 Census records which include a large range of information including demographic, socio-economic, self-reported health, housing and household and family structure data. Datasets are available for (a) Person (individual level), (b) Household (household-level) and (c) Non-Members (i.e. individual level information for all members of households with at least one NILS member). Variables include:

 

• age, sex and marital status
• religion and community background
• family, household or communal establishment type
• housing, including tenure, rooms and amenities
• country of birth, ethnicity
• educational qualifications
• economic activity, occupation and social class
• migration (between 2000 and 2001)
• limiting, long-term illness, self-reported general health, care-giving
• travel to work

To access the Census 2001 Individual and Household Questionnaires please click here.

1991 Census Datasets

An electronic link to the 1991 Census is also included in the NILS: an overall match rate of c. 70% has been achieved. Plans to increase the match rate of NILS members to the 1991 Census returns are currently under review. More updates to follow.

2011 Census Datasets

The linkage of the 2011 Census returns to the NILS has been identified as a key strategic objective by the NILS Steering Group. This will ensure that a database comprising 28% of the NI population has full information from two censuses (2001 and 2011), significant information from 1991 census and 14 years of vital events data.  For more information on developing potential projects, and the data release timetable, please contact the NILS-RSU. More updates to follow.

For general information and to access the 2011 Census Individual and Household Questionnaires please click here.

Vital Events Datasets

NILS sample members are also linked to vital events data, such as births and deaths, from the General Register Office for Northern Ireland. Datasets routinely linked include:

Births (1997 – 2009)

• New births into the NILS sample
• Births to NILS sample mothers and fathers

Variables include: parents’ duration of marriage, employment and occupation status, age, social class, address, age, marital status, previous births, month and year of occurrence and registration, place of birth and sex.

Deaths (2001 – 2009)

• Deaths of sample members 2001-2009

Variables include:  age, address, month and year of occurrence and registration, employment status, occupation code, social class, marital status, main cause of death, place of death.

Further possible linkages (available pending researcher demand) include:

• infant deaths to NILS members
• infant deaths of NILS members
• stillbirths to NILS members
• marriages
• widow(er)hoods

Property Datasets

NILS sample members are also linked the Land and Property Services for Northern Ireland database for 2001 to 2010. Variable include:

• Anonymised Unique Property Reference Numbers and Settlement Classifications (restricted access)
• Capital Value for residential properties (based on the 2005 rating valuation undertaken for Northern Ireland in 2005)
• Property characteristics including: number of rooms, habitable/ancillary space, year property built and type of parking

Area-Based Characteristics

Contextual and geographical indicators can also be linked to the NILS and NIMS databases including urban and rural settlement classifications and the Northern Ireland Multiple Deprivation Measure rankings. Analysis can be performed at a number of administrative geographies, such as Super Output Areas (c. 2000 population). However, because low geographical levels may lead to low numbers of observations, they may require special attention to issues of disclosure and confidentiality.

Users Own Datasets

Researchers may wish to have external data attached to their extract, for example linking data to specific event dates to identify flu epidemics. Researchers must clearly outline requirements they may have in relation to attaching external data to their NILS data extract.

Distinct Linkage Projects

The NILS and NIMS have received ethical approval for all research on migration, fertility, mortality and inequalities and can routinely link to the datasets outlined above.  There is also the potential to link to other administrative datasets, such as health and social care, for specially defined one-off studies.  These are subject to additional legal and ethical scrutiny and privacy protection protocols. Examples include cancer screening, prescribing and dental services data. For further information please contact the NILS-RSU.