An initial multi-stage sample of addresses has been chosen by means of the RANSAM sampling procedure (Whelan 1979) which was developed by the Economic and Social Research Institute (ESRI) based on the Irish Geodirectory, a comprehensive listing/mapping of residential addresses in Ireland compiled by the Ordinance Survey Office. Each address in the country has an equal probability of selection from the sample list of addresses.
A nationally representative sample of at least 8,000 adults aged 50 and over, resident in Ireland, was selected using a population sift. The selected addresses were visited by an interviewer from Ipsos MORI and all persons aged 50 or over (and their spouses/partners of any age) were canvassed to participate in the survey. Over 8,500 participants took part in Wave 1 of the study.
Fieldwork involved interviews using computer-aided personal interviewing (CAPI) techniques and either a visit by the respondent to a TILDA Health Assessment Centre, where appropriate medical measurement facilities were available, or a visit to the respondents' home by a qualified research nurse to take physical measurements and bio-medical samples. All respondents were also requested to fill out a self-completion questionnaire.
Participants in the first wave of the TILDA study will have a follow-up interview every two years and a health assessment every three to four years for a ten year period.