Design & Sample
The input of two groups is critical to the design of the study, people with ID and an international scientific committee. In pursuit of inclusion and participation people with an ID are included in every stage of the development, design, implementation and evaluation of all waves of the study. Their input helps in the design of pictorial explications to complement all written material increasing the accessibility of the study's questionnaires. An international scientific committee with extensive experience working with people with intellectual disability advises on the development of all protocols and provides input on both ID-specific content and advises on the opportunities for comparability with international studies. IDS-TILDA has been granted full ethical approval for all waves of the study by Trinity College Dublin Faculty of Health Sciences Research Ethics Committee. This follows the completion of an extensive pilot (McCarron et al., 2010), which tested the survey instruments and fieldwork approach.
The National Intellectual Disability Database (NIDD) collates information on all people with an ID in the Republic of Ireland who are eligible for or receive services. Currently, there are in excess of 26,066 people with an ID registered with the NIDD (Kelly et al., 2010). The population includes persons at all levels of ID, and the full range of residential circumstances. Each person with an ID is assigned a personal identification number (PIN) when registered with the NIDD. Permission to use the NIDD as a sampling frame was granted after review by the NIDD Committee. A nationally representative sample was then drawn of people with an intellectual disability aged 40 years and over. Staff at NIDD, consistent with inclusion/exclusion criteria, randomly selected 1,800 'PINs'. The approach recognized that a 50% response rate or less is commonly reported in social research (O'Brien et al., 2006) and so successful recruitment of 750 to 850 people with ID aged 40 years and over from across Ireland was anticipated. NIDD released the PIN numbers of potential participants to the regional disability database administrator (RDDA) who ensured that information was correct and the person identified was still registered on the NIDD. To preserve confidentiality prior to the completion of consent, invitation packs were provided by IDS-TILDA to each RDDA and the RDDA addressed and posted the pack to the person associated with each PIN received. Invitation packs contained summaries explaining the project and consent forms, including easy read versions, directed to the person with ID and to families and support staff. Concurrently, IDS-TILDA team members were conducting information sessions with services providers, advocacy organizations and gatherings of families and of people with ID and advertising material on the study (e.g. DVD, information leaflets, posters etc) was distributed. IDS-TILDA staff also explained the forthcoming packs and answered queries or concerns expressed by people with ID, families, staff and services. Services were also encouraged to identify a link person with whom IDS-TILDA team members would liaise in setting up interviews once consents were returned to the IDS-TILDA team.