General population-based cohort
The Northern Ireland Longitudinal Study (NILS) is a large-scale, representative data-linkage study created by linking data from the Northern Ireland Health Card Registration system to the 1981, 1991, 2001 and 2011 Census returns and to administrative data from other sources. These include vital events registered with the General Register Office for Northern Ireland (such as births, deaths and marriages) and the Health Card registration system migration events data. The result is a 30 year plus longitudinal data set which is regularly being updated. In addition to this rich resource there is also the potential to link further Heath and Social care data in our distinct linkage projects (DLPs).
Selection into the study is based on birth date (day and month): 104 dates throughout the year were selected and if an individuals date of birth coincided with one of these they were included in the sample. The sample is large – c. 28% of the Northern Ireland population (approximately 500,000 individuals and accounting for approximately 50% of households).
The Northern Ireland Mortality Study (NIMS) is a large-scale data linkage study that links the 1991, 2001 and 2011 Census returns for the whole of the enumerated population (approximately 1.6 million individuals) to subsequently registered mortality data from the General Register Office (GRO). While larger than NILS it is more limited in scope, focusing only on the linkage of mortality data. It allows researchers to focus on more detailed analyses of specific cause of death, some of which may not be possible in NILS because of small numbers in sub-populations and the analysis of less common causes of death (e.g. accidental death). The NIMS dataset is recommended to researchers whose primary interest is in mortality in Northern Ireland. These data are maintained under the same conditions as the NILS and is accessible only under the same constraints.