1. Choosing Core NILS data and its impact on Research
Rónán Adams
Máire Brolly
NILS User Forum
11th December 2009

2. Aims: Understand the structure of the NILS
Understand the level/impact of Census Imputation and List Inflation
Understand the research implications

3. Identifying the Core NILS data
requirement to have a core data source
coverage of the data source
complete information on dates of birth
existing linkages between the data sources

4. Core Data Set Options: Data sets in Research Proposal – Agreement
Census
Health Card Registrations (CHI)
Issues:
Census Office only require Age
Any missing day/month Imputed to 1st
1st too high, all other dates too low
Person imputation (95%)
Health Card registrations
List Inflation (105%)

5. Existing Links between Data Sources
NICR Data
GRO Deaths
Central Health
Index
GRO Births
2001 Census
Records

6. Proposed Links between Data Sources
NICR Data
GRO Deaths
Central Health
Index
GRO Births
2001 Census
Records

7. NILS/NIMS NILS c28% of population
Sample members from Health Card Registrations
List Inflation an issue
Census Imputation
NIMS
100% of deaths
Census members linked to deaths
Only enumerated people can be linked

8. Sample Selection in NI 104 dates – 100 NI, 4 E&W
For each download (6 monthly)
Is the DDMM of the DOB a NILS date? If so then they are in the sample
NILS sample – a person who has ever been in one of the 6-monthly downloads

9. Contextual Data NILS Core Data Events Health Card Registrations 2001
Census
Database
Deaths
Health Card
Registrations
Key demographic
information on NILS
members
(514,000 live)
@ Census Date
Births to Mothers
Births to Fathers
1991 Census
Stillbirths &
Infant Deaths
Births Data
(baby linked to
Birth Registration)
1997 births onwards
Migration
(Immigrants,
Emigrants,
Re-Entrants
& Within NI Movers)
New members
(c40,000)
POINTER
Address Database
VLA/Rating Data

10. The 3 LSs NILS E&W LS SLS Number Dates 104 4 20 Size 500,000 (28%)
500,000 (1%)
300,000 (5%)
Start Date
2001
1971
1991
Number of Censuses 1 2
Source
Health Card Registration
Census + GRO Births + NHSCR Immigrants
Includes Enumerated, Imputed and List Inflation – can look at enumerated only
Enumerated only

11. SG Discussion LS and SLS reps included on NILS SG
Recognition and Agreement between 3 LSs
NILS methodology would allow future ‘UK’ analyses

13. List Inflation 83,206 Imputed Records Imputed Records Health Card
Registrations
Central Health
Index
All Live Patients
(4th May 2001)
1,768,473
List Inflation
83,206
4.7%
Published
2001
census
population
One Number
(29th April 2001)
1,685,267
Imputed Records
81,626
Imputed Records
81,626
4.6%
Enumerated
2001
census
population
(29th April 2001)
1,603,641
Enumerated
2001
census
population
(29th April 2001)
1,603,641
90.7%

14. NOT 4.6% & 4.7% across all groupings
Imputation and List Inflation: different profiles by age, gender, geography and other characteristics
NOT 4.6% & 4.7% across all groupings

15. The very young Age All Patients Published Census Enumeration
Imputation
Inflation
16321
21683
19542
2141
-5362 1
22170
22363
20860
1503
-193 2
23389
23264
21757
1507
125 3
23800
23584
22142
1442
216

16. Female vs Male

17. All People

18. Imputation

19. List Inflation

20. Geographical Area Small geographies Urban – Rural Administrative Areas
Settlements
Deprivation

21. Urban/Rural

22. Urban/Rural

23. Assembly Areas / Parliamentary Constituencies

24. MDM - Deciles DECILE Enumerated Imputed List Inflation % LI, Imp
Least Deprived
157,974
5,710
2,525 5%
156,166
5,375
-4,652 0%
158,522
6,122
-273 4%
162,774
6,546
1,150
162,128
8,177
2,133 6%
166,973
8,897
3,644 7%
162,667
7,946
10,109
10%
162,913
9,324
11,422
11%
159,247
10,095
23,688
18%
most Deprived
154,277
13,434
33,458
23%

25. List Inflation Census Imputation Age, gender, geographical area
All Census characteristics

26. Imputation level – Marital Status

27. Imputation level – Economic Activity

28. Imputation level – Community Background

29. Summary
Characteristics of List Inflation & Imputation are different from Enumerated
Highest in deprived, urban areas
Affects males more than females
Affects year olds most
Unemployed, students, living alone

30. Impact on NILS Imputed people can’t be linked – no names, DOBs etc.
List inflation people unlikely to be on other administrative data (births, deaths, …)
Can only expect to link a proportion of population

31. Estimate for NILS 28% sample
4.7%
Health Card
Registrations
with
NILS Date
Central Health
Index
All Live Patients
(4th May 2001)
508,279
List Inflation
23,914
Don’t know who is ‘list inflation’
Don’t know who is ‘imputed’
Assume 28% is representative
4.6%
Imputation
23,460
90.7%
Enumerated
460,904

32. NILS Match Rate (MCR-Census)
4.7%
Health Card
Registrations
with
NILS Date
Central Health
Index
All Live Patients
(4th May 2001)
508,279
List Inflation
23,914
List Inflation
23,914
4.6%
Imputation
23,460
Imputation
23,460
90.7%
Enumerated
460,904
Unmatched
13,447
Matched
447,457
88%
Match
Rate
97%
Match Rate
Adjusted

33. What % can we expect to match?
Core NILS – Census
LI, Imp
91%
Core NILS – Births LI
95%
Core NILS – Births – Census
Core NILS – Deaths
Core NILS – Deaths – Census
NIMS – Deaths – Census
Imp

34. Hypothetical Example General Fertility Rate – 8,000 births
number of births per 1,000 women aged 16-44
8,000 births
NILS members (16-44)
130,000
GFR = 62.1 per 1,000
NILS members with Census link (16-44)
110,000
GFR = 72.7 per 1,000
‘true’ estimate
120,000
GFR = 67.2 per 1,000

35. Dental Registrations - Males

36. Dental Registrations - Females

37. Dental Registrations – Relative differences

38. Summary List inflation & imputation are issues
Imputation can be measured – lots of information
LI cannot be easily measured – limited information
Match rates cannot be easily determined
Characteristics of imputed and list inflation different from ‘normal’ population
Need to consider impact on your research

39. Aim: Understand the structure of the NILS
Understand the level/impact of Census Imputation and List Inflation
Understand the research implications

40. Choosing Core NILS data and its impact on Research
Rónán Adams
Máire Brolly

41. CSA
FPS
CHI
NHAIS
BSO
H&C, CHIN
HEALTH CARD REGISTRATIONS