The Northern Ireland Longitudinal Study:

data linkage, research potential and application

Gemma CatneyCentre for Public Health, Queen’s University Belfast

Meeting of the Royal Statistical Society Leeds/Bradford, 26th January

Presentation outline• Part one: The NILS – background to the data and

their linkages• Part two: Research application – Segregation and

health in NI– Segregation and (ill)health

• Minority/majority status– ‘Religious’ concentration in Northern Ireland– Hypotheses, data, methods– Results

• Logistic regression (outcome: poor GH), pop. concentrations• Cox proportional hazards (outcome: all-cause mortality)• Segregation indices and poor general health

– Discussion, conclusions, future work

Part one: The NILS – background to the data and

their linkages

Background to the NILS and NIMS

1. Research-Driven• Cross-sectional studies: no information on change over time• Other UK LS• Other international mortality-based LS• Health and socio-demographic profile of NI

2. Legislation• Confidentiality protected, and managed by NISRA, under

Census legislation

3. Funding• Infrastructure funded by the Health and Social Care R&D

Division and NISRA• Research support function funded by ESRC and NI

Government (OFMDFM)

Overview of the NILS and NIMS1. Northern Ireland Longitudinal Study (NILS) – c. 28% representative

sample of NI population (c. 500,000), based on health card registrations, linked to:• 2001 Census returns• vital events (births, deaths and marriages) • demographic & migration events• distinct Health & Care datasets

2. Northern Ireland Mortality Study (NIMS) - enumerated population at Census Day (c.1.6 million), linked to: • 2001 Census returns • subsequently registered mortality data

Both NILS and NIMS linked to contextual and area-based data:• capital value of houses and property attributes• geographical indicators• settlement classifications• deprivation measures

Datasets routinely linkedCensus Dataset 2001 GRO Vital Events Datasets 1997-2007

Variables include:Age, sex and marital status Religion and community backgroundFamily, household or communal typeHousing, including tenure, rooms and amenitiesCountry of birth, ethnicity Educational qualificationsEconomic activity, occupation and social classMigration (between 2000 and 2001)Limiting, long-term illness, self-reported general health, caregivingTravel to work

- New births into the sample - Births to sample mothers and fathers - Stillbirths to sample mothers - Infant mortality of children of sample mothers and fathers - Deaths of sample members 2001-2007 - Marriages 2004-2006 - Widow(er)hoods 2004-2006

LPS Property Data 2010 Health Card Registration Datasets 2001-2010

Capital and rating value (based on 2005 valuation exercise)

Variables include: - Household characteristics (no. of rooms, property type, floor space, central heating) and valuation - Estimated capital value

- Demographic data: age, status and location

- Migration events: immigrants added to the sample emigration of sample members re-entry of sample members to NI migration within NI

Research based on the NILS/NIMS• Health and mortality

• Temperature-related mortality and housing • Socio-demographic and area correlates of suicides • Distribution of cancer deaths in Northern Ireland by population and household

type • Variations in alcohol-related deaths in Northern Ireland

• Demographic trends• Fertility in the short-run in Northern Ireland• Lone mothers at time of birth: who are they?• Fertility levels and future school populations• Describing and modelling internal migration• Deprivation & ill-health: a comparison of Scotland and NI

• Education, employment and income• Unemployment and permanent sickness in NI• Pervasive area poverty: modelled household income • House value as an indicator of cumulative wealth in older people

• Area-based analyses• Rural aspects of health• Population movement and the spatial distribution of socio-economic and health

status• Residential concentration/segregation and poor health

NILS Research Support Unit

• Based at the Centre for Public Health (QUB) and NISRA HQ (McAuley House)

• Support: 2 full-time and 1 half-time Research Support Officers• Established April 2009

Remit:

• raise awareness of the NILS research potential;• assist with development of research ideas and projects;• facilitate access to NILS data;• training & advice in use and analysis of NILS datasets;• promote policy relevance; and• enhance NILS research capacity

Research support

Matching process

• NIMS database based on 1.6m pop. at 2001 Census

• GRONI deaths data added to NIMS database on a six-monthly basis

• 3-stage matching process:• exact computer matching• fuzzy computer matching• detailed manual searching

Linkage rates close to 100% not possible for NIMS – why?

1. Non-enumeration at Census: One Number Census methodology: imputation for adjusted est. total Imputation varies by age, gender and geographical area In NI enumerated 2001 Census total was 1,603,641 - an additional 81,626

people were imputed = overall imputation rate of 4.6%.

2. People who came to NI after 2001 and subsequently died: selective unrecorded migration

3. Differences between the info collected on census form and death certificate

Record Linkage: Issues and Biases

Study on potential biases:O’ Reilly, D., Rosato, M. & Connolly, S. (2008) Unlinked vital events in census-based longitudinal studies can bias subsequent analysis.

Journal of Clin. Epid. 61: 380-385.

What are the characteristics of people whose events are not linked into the LS datasets?

What does this mean for analyses using the LS?

Record Linkage: Issues and Biases

Record Linkage Rates 2001-2005• 59,396 deaths available to be linked from 2001-2005

• 6% deaths (3,392) could not be matched

Process Number (%)All death records NI 59,396

Exact matches 45,496 (80.6)Fuzzy matches 4,491 (8.0)

Manual matches 2,093 (3.7)

Linkage through HCR

951 (1.7)

Unlinked 3,392 (6.0)

Characteristics of matched and non-matched deaths

Based on data from death records (multivariate log reg):

• Year of registration

• Socio-demographic details• age, sex, marital status, social class (NS-SEC)

• Place of death • home, hospital, nursing/residential home

• Area in which they lived (SOA)• Deprivation (income domain)• Urban/rural• Population density• Imputation

• Cause of death

Variation according to demographic characteristics (Outcome: unmatched death, 2001-2006)

Aged less than 65 Aged more than 65Sex Deaths OR Deaths OR

Male 8,130 1.00 25,443 1.00Female 4,941 0.63 *** 31,775 0.92*

Marital statusMarried 7,398 1.00 19,450 1.00

Single 3,549 1.57 *** 8,873 2.83 ***Widowed 776 1.40 *** 27,758 1.97 ***

Sep/Divorced 1,348 2.52 *** 1,137 3.30 ***Place of death

Home 6,066 1.00 13,378 1.00N/R home 1,009 1.05 12,771 2.00 ***

Hospital 5,996 0.80 *** 31,069 1.28 ***

*** P<0.001; ** P< 0.01; * P<0.05

Variation according to relative deprivation (Outcome: unmatched death, 2001-2006)

Aged less than 65 Aged more than 65

Deaths Odds ratios Deaths Odds ratios

Least Deprived

1,831 (6.8%)

1.00 10,543 (5.7%)

1.00

2nd 2,137 (8.8%)

1.19 11,103 (5.4%)

0.90

3rd 2,554 (9.5%)

1.20 11,933 (6.0%)

0.93

4th 2,901 (10.4%)

1.20 11,534 (5.2%)

0.84 *

Most Deprived

3,530 (16.0%)

1.78 *** 11,374 (7.2%)

1.23 **

*** P<0.001; ** P< 0.01; * P<0.05

Variation by cause of death (Outcome: unmatched death, 2001-2006)

All ages Under 65 years old

Deaths (%unmatched) Deaths (%unmatched)

All causes 70,289 (6.9%) 13,071 (11.1%)

I.H.D 13,970 (5.6%) 2,064 (9.4%)

Stroke 7,211 (6.8%) 542 (8.9%)

Respiratory Disease 9,722 (7.0%) 802 (9.9%)

Cancer 18,572 (5.6%) 4,846 (8.1%)

All External causes 2,634 (15.2%) 1,648 (20.3%)

Accidents 1,719 (12.3%) 830 (18.2%)

Suicides 702 (19.9%) 649 (21.4%)

Other Causes 12,840 (8.9%) 2,579 (13.6%)

• Research conclusions: small proportion of events are not linked – biases:

– increase in months immediately after Census Day 2001– increase with ‘distance’ from the Census– are non-random and more frequent in …

• younger males, older females• people who are perhaps more socially isolated• amongst residents of nursing/residential homes• deprived areas• where enumeration is low

Non-linkage may limit the ability to study some causes of death and potentially lead to an underestimation of social gradients

Record linkage: issues and biases

Statutory obligation to record death events. Complete & good quality data:

long experience of use for mortality analyses andthere will be biases in every linkage study ≠100%:

this research shows that biases can be quantified

Small number problems i.e., falling death rates, population sub-groups (minority ethnics), cause-specific mortality (suicides, trauma & specific cancers)

yet: can increase length of follow-up study, aggregate sub-populations & increase cohort size

So there are potential biases, however...

Part two: Research application – segregation

and health in NI

The help provided by the staff of the Northern Ireland Longitudinal Study and Northern Ireland Mortality Study (NILS and NIMS) and the NILS Research Support Unit is acknowledged. The NILS and NIMS are funded by the Health and Social Care Research and Development Division of the Public Health Agency (HSC R&D Division) and NISRA. The NILS-RSU is funded by the ESRC and the Northern Ireland Government. The authors alone are responsible for the interpretation of the data.

Corresponding author: g.catney@qub.ac.uk

More information on NILS/NIMS data: www.nils-rsu.census.ac.uk

Acknowledgements