The Intellectual Disability Supplement to the Irish Longitudinal Study on Ageing (IDS-TILDA) is a longitudinal study researching ageing in Ireland among people with an intellectual disability aged 40 and over. This study is the first of its kind in Europe, and the only study able to directly compare the ageing of people with an intellectual disability with the general ageing population. The underpinning values of IDS-TILDA are inclusion, choice, empowerment, person centred, the promotion of people with intellectual disability, the promotion of best practice and to contribute to the lives of people with intellectual disability. The objectives of IDS-TILDA are: to understand the health characteristics of people ageing with an intellectual disability; to examine the service needs and health service utilization of people ageing with an intellectual disability; to identify disparities in the health status of adults with an intellectual disability as compared to The Irish Longitudinal Study on Ageing’s (TILDA) findings for the general population; and to support evidence-informed policies, practices and evaluation. IDS-TILDA provides much needed data on the health, social, economic and environmental circumstances of 753 people as they grow older and how their circumstances change over a period of time.

Probability: Simple random. The IDS-TILDA sample was drawn randomly from the population of adults aged 40 years and above on the National Intellectual Disability Database (NIDD). At the time of the Wave 1 interviews, the NIDD was an administrative database managed by the Health Research Board (HRB) and contained information on people with an intellectual disability in the Republic of Ireland who are registered with a service provider. For recruitment of the original sample at Wave 1, the dataset contained 26,066 individuals (Kelly et al. 2010). From this, the inclusion criterion of being aged 40 years across all levels of intellectual disability and living circumstances was applied. In total 1,800 individuals were randomly selected by NIDD staff; just over 1,600 of these were provided information and asked to participate in the study and 200 were kept in reserve. Written consent was obtained from 753 individuals (a 46% response rate), either directly by self- consenting individuals (38%, n=285) or by a family member or guardian for those who were unable to self-consent (62%, n=468). The final Wave 1 sample was demographically and geographically representative of the target population within the NIDD; it equated to 8.9% of the total eligible population at the time. Please note that the NIDD is now known as the National Ability Support System (NASS).

Face-to-face interview: CAPI/CAMI

Self-administered questionnaire: Paper