The method used to select partcipants for the NICOLAstudy was designed to ensure that the sample would be representative of the Northern Ireland population aged 50 and over.
Over 400,000 adddresses were identified as having a household member of 50 years or above. A method was used to provide a smaller random sample that provided an overall representation of the community in Northern Ireland. This resulted in over 14,000 addresses.
In the first Wave the selected addresses were visited by an interviewer from Ipsos MORI who initially confirmed that someone aged 50 or over lived within that household. All persons aged 50 or over (and their spouses / partner of any age) were asked if they would like to participate in the survey.