Ireland shares with other developed countries the prospect of rapid and sustained population ageing. The age distribution of the Irish population is undergoing a dramatic change at present and this trend is predicted to continue into the future.1 People are living longer, and older persons represent a larger proportion of the population. In Ireland, the proportion of the population aged ≥65 years has remained steady at ∼11% for the past 40 years. However, it is projected that this proportion will rise to 14% by 2021 and to 19% by 2031.2 The greatest increase will be in the oldest old, aged >80 years, which is expected to more than treble by 2036.2 This change in the demographic profile of the Irish population poses a major public health challenge. Unlike the situation in the USA,3,4 the UK5 and many other developed countries,6,7 there have been no large population-based cohort studies in Ireland to inform research on healthy ageing. Whereas a number of studies have provided population-based data on the health status of older people living in Ireland,8–10 many questions remain unanswered. The Irish Longitudinal Study on Ageing (TILDA) is a large prospective cohort study of ageing, which includes an assessment of the social, economic and health circumstances of community-resident older people living in Ireland. The study has been harmonized with leading international research so as to ensure adoption of best practice and comparability of results. The Irish government, The Atlantic Philanthropies and Irish Life plc have provided funding for the study. Ethical approval has been obtained from the Trinity College Dublin Research Ethics Committee. Recruitment for the first wave of TILDA began in October 2009 and fieldwork was completed in February 2011 when the target sample of more than 8000 participants had been achieved. The health assessment component (described below) is ongoing and will be completed by July 2011. The sampling frame is the Irish Geodirectory, a comprehensive and up-to-date listing and mapping of all residential addresses in the Republic of Ireland compiled by ‘an Post’ (the Irish Postal Service) and Ordnance Survey Ireland.11 An initial multi-stage probability sample of addresses was chosen by means of the RANSAM sampling procedure,12 developed by the Economic and Social Research Institute. Addresses were selected by means of a three stage process: (i) selection of first stage units (clusters which are subdivisions of District Electoral Divisions comprising between 500 and 1180 addresses) using proportionate stratification by socio-economic status (per cent in professional/managerial occupations), age structure (per cent of population aged ≥50 years) and geographical location. Selection of first stage units was based on probability proportionate to size, the size measure used being the estimated number of addresses containing a person aged ≥50 years in the cluster. (ii) Selection of a systematic random sample of fixed size (50 addresses) within each cluster. Each residential address in the country had an equal probability of selection. The selected addresses were randomly partitioned into two groups: an initial sample list of 25 600 addresses (40 addresses in each of the 640 clusters, Figure 1) for immediate issue and a reserve list of 6400 addresses (10 randomly selected from each of the 640 clusters). As the target sample size was achieved using the initial sample list, the reserve list was not utilized. A listing and location map of the selected residential addresses were provided to the social interviewers on Global Positioning System (GPS) devices which also had the coordinates of the selected addresses. Selected households with a unique address were sent a letter of invitation to participate in the study by post. Advance letters were hand delivered by the interviewers to those households with a non-unique address (∼40% of Irish addresses are non-unique and there is no national postcode or zipcode system). The letter of invitation was followed up after 1 week by a home visit from a member of the field staff to determine whether there was an eligible person living in the household. (iii) All household residents aged ≥50 years were eligible to participate in the study (primary respondent). The spouses/partners (of any age) of respondents were also invited to participate (secondary respondent). The sample was designed to give each household in the country an equal probability of selection and, since all members aged ≥50 years in each household were eligible, each person aged ≥50 years also had an equal probability of selection. The spouses aged <50 years were interviewed mainly to provide couple- or household-level data and will not in general be included in person-level analyses. Map of selected addresses—the location of the 640 clusters The study aims are broad and include: the description of the current economic, social and health circumstances of older people living in Ireland and the creation of a longitudinal database with a combination of social, economic and health data to allow the monitoring of changes in health and well-being over time and the exploration of the complex inter-relationships between numerous potential risk factors and protective factors and their impact on longevity and healthy ageing including for example: the role of early childhood experiences on physical and mental health in later life; the relationship between physical activity, obesity and frailty; the influence of mood disturbances including anxiety and depression on cognitive and physical health; and the effect of cognitive impairment on financial decisions around retirement. Participants were visited in their own homes by a member of the field staff. The interview component of the survey was undertaken by trained professional social interviewers. The interviewers used computer-assisted personal interviewing (CAPI) and entered responses directly into a laptop computer. The TILDA questionnaire includes detailed questions on socio-demographics, living standards, income and wealth, physical health, lifestyle and behaviour, social support and participation, use and perceived need for health and social care and attitudes to ageing (Table 1). Following completion of the interview, participants were asked to complete a self-administered questionnaire (Table 1) and were invited to participate in the physical assessment component of the study. The assessments take place in one of the two dedicated clinical assessment centres in Dublin and Cork, which are staffed by a team of trained study nurses. Participants are reimbursed for the cost of attending the centres. The duration of the clinical assessment is ∼150 min and includes—anthropometric measurements: height, weight and waist circumference; cardiovascular measurements: heart rate variability, blood pressure and pulse wave velocity; gait, balance and sensory measurements: timed up and go, gait assessment using a sensored mat, visual acuity and contrast sensitivity; bone and muscle strength: grip strength, heel ultrasound; cognitive measurements: global cognition, sustained attention, executive function, visual memory, speed of processing and assessment of macular degeneration: macular pigment optical density and retinal photograph (Table 2). TILDA-specific software has been developed to electronically capture all data collected in the clinical assessments and to transfer the data to a secure database. Where possible, the measurements are recorded directly and uploaded onto a file that is linked to the participants’ unique identifier. For those data items that require direct data entry (such as height and weight), the programme has built-in functions to avoid missing items and minimize errors. Respondents who are unable or refuse to attend a clinical assessment centre are given the option of a home visit by a study nurse for a subset of the clinic physical assessment (Table 2). All participants in the clinical and home assessments are asked to provide a sample of blood. Separate consent is obtained for participation in the physical assessment and the donation of the blood sample. For participants who agree to provide a blood sample, separate consent is requested for immediate analysis, long-term storage and genetic analysis. The consent allows for the blood to be used for unspecified research purposes that are of no direct benefit to the individuals. A total of 25 ml of non-fasting venous blood is collected into 3 vacutainers. At the end of each survey day, the blood samples are transported to a centralized laboratory in temperature-controlled shipping boxes that maintain the samples at 2–8°C for up to 48 h. Immediate analysis is undertaken for lipid profile as this result is provided in feedback to participants. At the central laboratory, the samples are centrifuged and then aliquoted into 10 bar-coded cryovials (8 plasma samples and 2 buffy coat) for storage at −80°C. It is planned that some of the samples will be transferred to nitrogen tanks for long-term storage at the end of the first wave of data collection. Summary of data collected in TILDA CAPI and Self-completion Questionnaire (SCQ) Demographic data Education Childhood health Migration history Marital status and marriage history Social circumstances Transfers to (and from) children Transfers to (and from) parents (Instrumental) activities of daily living Helpers Social connectedness Participation in social/recreation activities Relationship quality (SCQ) Employment and lifelong learning Employment situation Job history Lifelong learning Retirement and expectations Planning for retirement Expectations Income and assets Sources of income Assets Transport Transportation Driving Medications Health-care utilization Physical health Self-rated health Limiting long-standing illness/disability Sensory function Cardiovascular disease Non-cardiovascular chronic illness Falls/fear of falling/steadiness Chronic pain Incontinence Medical screening Mental health Self-reported mental health Depression Life satisfaction Anxiety (SCQ) Worry (SCQ) Loneliness (SCQ) Perceived stress (SCQ) Stressful life events (SCQ) Quality of life (SCQ) Cognitive health Self-rated memory Orientation Word-list learning (immediate and delayed recall) Verbal fluency Prospective memory Behavioural health Smoking Physical activity Sleep Alcohol (SCQ) Ageing perceptions (SCQ) Demographic data Education Childhood health Migration history Marital status and marriage history Social circumstances Transfers to (and from) children Transfers to (and from) parents (Instrumental) activities of daily living Helpers Social connectedness Participation in social/recreation activities Relationship quality (SCQ) Employment and lifelong learning Employment situation Job history Lifelong learning Retirement and expectations Planning for retirement Expectations Income and assets Sources of income Assets Transport Transportation Driving Medications Health-care utilization Physical health Self-rated health Limiting long-standing illness/disability Sensory function Cardiovascular disease Non-cardiovascular chronic illness Falls/fear of falling/steadiness Chronic pain Incontinence Medical screening Mental health Self-reported mental health Depression Life satisfaction Anxiety (SCQ) Worry (SCQ) Loneliness (SCQ) Perceived stress (SCQ) Stressful life events (SCQ) Quality of life (SCQ) Cognitive health Self-rated memory Orientation Word-list learning (immediate and delayed recall) Verbal fluency Prospective memory Behavioural health Smoking Physical activity Sleep Alcohol (SCQ) Ageing perceptions (SCQ) Summary of data collected in TILDA CAPI and Self-completion Questionnaire (SCQ) Demographic data Education Childhood health Migration history Marital status and marriage history Social circumstances Transfers to (and from) children Transfers to (and from) parents (Instrumental) activities of daily living Helpers Social connectedness Participation in social/recreation activities Relationship quality (SCQ) Employment and lifelong learning Employment situation Job history Lifelong learning Retirement and expectations Planning for retirement Expectations Income and assets Sources of income Assets Transport Transportation Driving Medications Health-care utilization Physical health Self-rated health Limiting long-standing illness/disability Sensory function Cardiovascular disease Non-cardiovascular chronic illness Falls/fear of falling/steadiness Chronic pain Incontinence Medical screening Mental health Self-reported mental health Depression Life satisfaction Anxiety (SCQ) Worry (SCQ) Loneliness (SCQ) Perceived stress (SCQ) Stressful life events (SCQ) Quality of life (SCQ) Cognitive health Self-rated memory Orientation Word-list learning (immediate and delayed recall) Verbal fluency Prospective memory Behavioural health Smoking Physical activity Sleep Alcohol (SCQ) Ageing perceptions (SCQ) Demographic data Education Childhood health Migration history Marital status and marriage history Social circumstances Transfers to (and from) children Transfers to (and from) parents (Instrumental) activities of daily living Helpers Social connectedness Participation in social/recreation activities Relationship quality (SCQ) Employment and lifelong learning Employment situation Job history Lifelong learning Retirement and expectations Planning for retirement Expectations Income and assets Sources of income Assets Transport Transportation Driving Medications Health-care utilization Physical health Self-rated health Limiting long-standing illness/disability Sensory function Cardiovascular disease Non-cardiovascular chronic illness Falls/fear of falling/steadiness Chronic pain Incontinence Medical screening Mental health Self-reported mental health Depression Life satisfaction Anxiety (SCQ) Worry (SCQ) Loneliness (SCQ) Perceived stress (SCQ) Stressful life events (SCQ) Quality of life (SCQ) Cognitive health Self-rated memory Orientation Word-list learning (immediate and delayed recall) Verbal fluency Prospective memory Behavioural health Smoking Physical activity Sleep Alcohol (SCQ) Ageing perceptions (SCQ) Summary of clinical measurements collected in the TILDA health assessment 1. Montreal Cognitive Assessment (MOCA) 2. Mini Mental State Examination (MMSE) Visual reasoning–CAMDEX Timed Colour Trails 1and 2 1. Montreal Cognitive Assessment (MOCA) 2. Mini Mental State Examination (MMSE) Visual reasoning–CAMDEX Timed Colour Trails 1and 2 aIf the difference between two measurements is >3 cm, a third measurement is required, with the values for the last two measurements recorded. bManual task is carrying a glass of water. cCognitive task is reciting alternate letters of the alphabet starting at A. Summary of clinical measurements collected in the TILDA health assessment 1. Montreal Cognitive Assessment (MOCA) 2. Mini Mental State Examination (MMSE) Visual reasoning–CAMDEX Timed Colour Trails 1and 2 1. Montreal Cognitive Assessment (MOCA) 2. Mini Mental State Examination (MMSE) Visual reasoning–CAMDEX Timed Colour Trails 1and 2 aIf the difference between two measurements is >3 cm, a third measurement is required, with the values for the last two measurements recorded. bManual task is carrying a glass of water. cCognitive task is reciting alternate letters of the alphabet starting at A. The interview component of the study will be repeated every 2 years with the clinical assessment component repeated every 4 years. Funding has been secured for the data collection components of the study until 2016. The questionnaire was administered to 8507 individuals (6282 primary respondents and 2225 secondary respondents) including 8178 respondents aged ≥50 years and 329 younger partners of eligible individuals. The response rate is the proportion of selected households including an eligible participant from which an interview was successfully obtained. Interviewers were sent to all of the initially allocated 25 600 addresses. Of these, 22 321 were occupied residential addresses. At 11 819 addresses, contact was made and it was determined that no person aged ≥50 years was at that address. In 9818, it was determined that there was a person aged ≥50 years. At 684 addresses, either no contact was made or contact was made, but it was impossible to determine whether there was anybody aged ≥50 living at that address. Based on those households in which eligibility was determined, it is estimated that 9818/(9818 + 11 819) × 684 = 310.4 of those households were eligible. The estimated number of selected eligible households is therefore 9818 + 310.4 = 10 128.4. Successful interviews were obtained in 6282 households, giving an adjusted response rate of 62%. The response to the self-completion questionnaire is ∼84%. Over 80% of CAPI respondents have agreed to a physical assessment and these are scheduled to be completed by July 2011. To date, over 6000 physical assessments have been completed and almost all physical health assessment participants have also provided blood samples. Comparison with the Irish population using data from the Quarterly National Household Survey (Table 3) demonstrates that individuals with lower levels of educational attainment are under-represented in TILDA, and there are minor differences in response rate among particular age and gender groups. Weights have been derived to allow for this differential non-response by age, gender and level of education. In the majority of analyses, the analytical unit is the individual respondent, but many analyses, primarily those in the social and economic domains, may use the household unit. All analyses will include an adjustment for clustering of responses at the household and geographical primary cluster levels. Comparison of TILDA cohort at Wave 1 with population in Irelanda aThe numbers for the population are from the Quarterly National Household Survey (QNHS), which is a large-scale, nationwide survey of households in Ireland conducted by the Central Statistics Office. Comparison of TILDA cohort at Wave 1 with population in Irelanda aThe numbers for the population are from the Quarterly National Household Survey (QNHS), which is a large-scale, nationwide survey of households in Ireland conducted by the Central Statistics Office. As the study sample is large and is nationally representative, the baseline prevalence rates are of interest for describing the current health and well-being of those aged ≥50 years in Ireland as well as for informing policy for determining future needs. A report of preliminary findings from TILDA was made available in May 2011.13 This report highlighted the heterogeneity of the health, economic and social circumstances of people aged ≥50 years living in Ireland. Strong socio-economic gradients in health were consistently observed, with those with greater asset wealth and more completed education being in substantially better health measured by self-reported health status, diagnosed disease and through objective measurement. Comparison of the objective measures of mental and physical health taken during health assessments with self-reports of diagnosed disease measured during the interview revealed a large burden of undiagnosed disease. Although older people did make greater use of many health-care services, health and not age was by far the greater independent determinant of health-care utilization. Descriptive information on the health and well-being of the TILDA cohort are reported in Table 4. Analyses of associations between risk factors and characteristics and morbidity and mortality will begin in a number of years when a sufficient number of events have occurred. In addition to information on socio-demographic, behavioural and physical health factors collected at baseline, the role of risk in including lipid and and genetic also be and well-being of TILDA participants at Wave 1 by age and are as of of activity was using the Physical Questionnaire The of of items that the time physical activities to and and The people as or levels of physical activity and those who levels are of on the for Depression of on Anxiety and Depression and well-being of TILDA participants at Wave 1 by age and are as of of activity was using the Physical Questionnaire The of of items that the time physical activities to and and The people as or levels of physical activity and those who levels are of on the for Depression of on Anxiety and Depression The TILDA sampling a nationally sample and will allow the Irish population. The survey has been developed based on best international practice and has been harmonized with other large cohort studies of ageing. It has been and in two The clinical assessment component of the study includes detailed physical and cognitive assessments as well as a number of The comprehensive of the data will numerous questions to be and the of a broad of will allow inter-relationships of factors to be with adjustment of The of a and a clinical assessment has the of older and participants from the health assessment component of the Participants were to provide consent to participate in the study which will have in the of some individuals with cognitive impairment or Whereas the questionnaire include a detailed assessment of cognitive function, the of a clinical assessment to make a assessment of or other of TILDA will include interviews so that individuals who cognitive impairment or over the of the study and are no to to the will remain as study participants. The large number of items collected by the a strength, has the that in some the of questions asked for any one of has been data have not been in the first wave of data collection and this of data will to the role of status on determining health and the impact of health and economic circumstances on questions will be included in the questionnaire for the wave of the study and it may be to components in the blood sample. The major for the study was being aged ≥50 years and a residential address. As a the study home residents and those in other information on long-term care of older people in Ireland is However, the of Statistics that in people in in Ireland and over of these are aged ≥65 years are aged of residents are or The of residents has to an of the older population. However, as participants from home to will remain in the study and so over TILDA will be to the social, economic and health circumstances of home All collected data are and at the study research in the of Medical Trinity College Ireland. Following completion of data processing and preliminary analyses, the data will be from the Irish Social It is planned that these data will include of designed to for differential non-response to components of the study. for future be information be on the study or through to The Atlantic Philanthropies to the Irish Longitudinal Study of Irish Life plc and the Irish to the Irish Longitudinal Study of in Research support from a to The for Research from The Atlantic The is to the participants in the to members of the TILDA research the study and of