Imputation in the 2001 Census:
Implications for analysis using
the ONS Longitudinal Study
Julian Buxton
CeLSIUS
MOLS 2006: Methodology of Longitudinal
Surveys, 12-14 July
Outline
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The ONS Longitudinal Study
Imputation in the 2001 Census
Imputation in the LS
Personal variables
Household level variables
Relationship variables
Example of analysis
What is the ONS Longitudinal Study?
• 1% sample of population of England & Wales
• Selected if birthday falls on one of four days in each year
• Data from censuses and vital registration systems
• Initial sample from 1971 Census; updated with addition of
1% new births and 1% of immigrants
• Exits from LS are by death or recorded emigration (also
some loss to follow up). All records are retained
• Individuals linked from one census to another so for those
in the sample since 1971, census data from four censuses
now available
Study Structure
Entrants
New Births
1971
228,000
Immigrants
122,000
1981
1991
2001
Original
sample:
530,000;
selected from
1971 Census
534,000
sample
members
found at 1981
Census
543,000
sample
members
found at 1991
Census
540,000
sample
members
found at 2001
Census
Plus members
of household
Plus members
of household
Plus members
of household
Plus members
of household
Births to sample women 215,000
Widow(er)hoods
70,000
Cancer registrations
78,000
Events 1971 – 2002
Deaths
201,000
Embarkations
32,000
Imputation in the 2001 Census
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Edit & Donor Imputation System (EDIS)
Edit
Imputation
One Number Census
“Census 2001 Review & Evaluation
Edit & Imputation: Evaluation Report 2003”
Imputation in the LS at 2001 Census
•Extract of all potential LS members from 2001
Census
•Traced at NHSCR and matched with current LS
records
•2001 Census Initial Extract containing post-edit data
•2001 Census Full Extract containing imputed data
•Imputation flags created and added to database
•No One Number Census imputations included
Personal variable Imputation rates in the 2001 Census and the LS
2001 census
Population
Imputation
000's
rate (%)
49,359
0.56
49,359
0.44
49,359
0.32
48,848
2.91
48,848
3.92
35,367
6.09
21,741
3.48
Age
Sex
Marital status
Ethnic group
Long-term illness
Highest qualification
Occupation (Cur work)
NS-SEC
Relationship to Person 1
28,065
4.73
Source:
2001 Census data from
"Census 2001 Review & Evaluation - Edit and imputation:
ONS Longitudinal Study
Population
539,879
539,879
539,879
538,026
538,026
391,841
244,104
369,784
304,380
LS
Imputation
rate (%)
0.20
0.40
0.24
2.80
3.83
6.05
3.29
12.89
4.62
Evaluation Report"
Household level variable Imputation rates for LS members
2001 Household level variable Imputation rates
Total in LS
%
Accommodation type
529,844
2.48
Number of rooms
529,844
4.82
Number of cars
529,844
2.37
Tenure
529,844
3.19
Owns/Rents
529,844
2.99
Landlord
142,280
2.82
Number of imputed household level variables
Number Total in LS
%
0
475,727
89.79
1
29,228
5.52
2
10,274
1.94
3
3,080
0.58
4
2,333
0.44
5+
9,202
1.74
Total
529,844
100
Excludes Communal Establishments
Source: ONS Longitudinal Study
Relationship Matrix
Name of Person 1
Name of Person 2
Name of Person 3
First name
First name
First name
Surname
Surname
Surname
Relationship of Person 2
to Person:
1
Relationship of
Person 3
to Person:
Husband or wife
Husband or wife
ENTER NAME OF PERSON 1
ABOVE
Partner
Partner
Son or daughter
Son or daughter
Step-child
Step-child
Brother or sister
Brother or sister
Mother or father
Mother or father
Step-mother or step-father
Grandchild
Step-mother or stepfather
Grandchild
Grandparent
Grandparent
Other related
Other related
Unrelated
Unrelated
1
2
Relationships
Three levels
• Personal relationships (relationships
between LS member and other
household members)
• Family relationships (any relationships
in the family of the LS member)
• Household relationships (any
relationships in the household of the LS
member
A family
“A group of people consisting of a married
or cohabiting couple with/without child(ren),
or a lone parent with child(ren)”.
A household
“One person living alone, or a group of
people (not necessarily related) living at the
same address with common housekeeping”.
Total number of Imputed Personal Relationships
No. of imputed
relationships
N
0
1
2
3
4
5+
Total
419,629
27,069
10,466
4,680
2,067
388
464,299
Personal
%
Relationship
Imputation rate
90.38
5.83
9.66
2.25
1.01
0.45
0.08
100
Personal Relationship Imputation rates by household size
No. in household
%
2
2.7
3
13.81
4
10.08
5
13.09
6
20.86
7
26.79
8
28.34
Excludes Communal Establishments
and those in households of 1 person
9
32.59
Source: ONS Longitudinal Study
10+
40.83
Family relationship Imputation
rate (Households of 2 or more)
%
11.83
Family Relationship Imputation
rates by household size
No. in household
2
3
4
5
6
7
8
9
10+
%
2.26
16.99
12.63
16.63
28.82
35.48
37.6
42.64
50.26
Excludes Communal Establishments
and those in households of 1 person
Source: ONS Longitudinal Study
Household relationship Imputation
rate (Households of 2 or more)
%
12.99
Household Relationship Imputation
rates by household size
No. in household
2
3
4
5
6
7
8
9
10+
%
2.7
18.46
13.52
18.32
31.58
40.18
43.96
49.1
65.17
Excludes Communal Establishments
and those in households of 1 person
Source: ONS Longitudinal Study
Example – Factors associated with
LLTI in 2001
• Study population – those present at 91
and 01, no LLTI in 91
• Aged 16-74 in 2001
• Factors - Housing Tenure, Highest
qualification and NSSEC at 2001
Factors associated with Limiting Long-term Illness in 2001
TENURE at 2001 (Odds Ratios & Sample Sizes)
No imputed values
Owned
Not Owned
1
1.70
297,273
Imp values as Owned
1
1.68
303,192
Imp values as Not Owned
1
1.70
303,192
HIGHEST QUALIFICATION at 2001
No imputed values
Qualifications
No Qualifications
1
2.97
291,690
Imp values as Quals
1
2.72
303,192
Imp values as No Quals
1
3.00
303,192
NSSEC at 2001
No imputed values
Prof & Manag
Intermediate
Routine & Man
1
1.26
1.69
Source: ONS Longitudinal Study
273,652
Imp values as Prof & Man
1
0.87
1.17
303,192
Imp values as Rout & Man
1
1.26
1.94
303,192
www.celsius.lshtm.ac.uk
Emily Grundy
Chris Marshall
Jo Tomlinson
Andy Sloggett
Julian Buxton
Lynda Clarke
General enquiries:
celsius@lshtm.ac.uk
020 7299 4634