Introduction to methodological
issues in LS ethnicity research
Julian Buxton
Bola Akinwale
Issues
• Sample sizes
• Item imputation in 2001
• Change in recorded ethnic group, 1991-2001
• Loss to follow-up
Ethnicity in the LS
• 1971 Census: Country of birth, parental COB
• 1981 Census: Country of birth
• 1991 Census: Ethnicity, Country of birth
• 2001 Census: Ethnicity, Country of birth and
religion (voluntary)
Table 1 – Ethnic group at 2001 (all people)
2001 Census LS traced
sample
N
%
WHITE
White British
467,822
White Irish
6,311
Other White
12,835
MIXED
White & Black Caribbean
2,384
White & Black African
780
White & Asian
1,882
Other Mixed
1,496
ASIAN or ASIAN BRITISH
Indian
12,487
Pakistani
8,350
Bangladeshi
3,277
Other Asian
2,606
BLACK or BLACK BRITISH
Black Caribbean
4,837
Black African
3,993
Other Black
926
CHINESE or OTHER ETHNIC GROUP
Chinese
2,213
Other Ethnic Group
2,174
TOTAL
534,373
2001 ONC population
N
%
87.5
1.2
2.4
45,533,741
641,804
1,345,321
87.5
1.2
2.6
0.4
0.1
0.4
0.3
237,420
78,911
189,015
155,688
0.5
0.2
0.4
0.3
2.3
1.6
0.6
0.5
1,036,807
714,826
280,830
241,274
2.0
1.4
0.5
0.5
0.9
0.7
0.2
563,843
479,665
96,069
1.1
0.9
0.2
0.4
0.4
100.0
226,948
219,754
52,041,916
0.4
0.4
100.0
Source: Table S01.6 2001 LS Sampling Fractions by sex and ethnic group
Table 2 – Religion at 2001
2001 LS traced sample
2001ONC population
Christian
Buddhist
Hindu
Jewish
Muslim
Sikh
All other religions
No religion
Religion not stated
N
384,462
1,486
6,251
2,632
17,586
4,614
1,501
76,093
39,748
%
71.9
0.3
1.2
0.5
3.3
0.9
0.3
14.2
7.4
N
37,338,486
144,453
552,421
259,927
1,546,626
329,358
150,720
7,709,267
4,010,658
%
71.7
0.3
1.1
0.5
3.0
0.6
0.3
14.8
7.7
TOTAL
534,373
100.0
52,041,916
100.0
Source: Table S01.5 2001 LS Sampling fractions by sex and religion
Table 3 – Country of birth at 2001
England
Scotland
Northern Ireland
Wales
Rest of Europe
AFRICA
ASIA
NORTH AMERICA
SOUTH AMERICA
OCEANIA
Other
TOTAL
2001 LS traced sample
N
%
445,054
83.3
8,028
1.5
2,221
0.4
28,570
5.3
15,154
2.8
2001 ONC population
N
%
43,566,005
83.7
818,966
1.6
222,975
0.4
2,798,465
5.4
1,491,939
2.9
7,866
20,893
4,088
757
1,288
454
1.5
3.9
0.8
0.1
0.2
0.1
808,940
1,594,302
466,995
73,785
158,488
46,347
1.6
3.1
0.9
0.1
0.3
0.1
534,373
100.0
52,047,207
100.0
Source: Table S01.4 2001 LS Sampling fractions by sex and country of birth
Table 4 – Ethnic group at 1991 (all people)
1991 LS traced sample
White
Black Caribbean
Black African
Black Other
Indian
Pakistani
Bangladeshi
Chinese
Other Asian
Other
N
499,853
5,220
2,001
1,723
11,180
6,104
2,385
1,641
2,071
2,837
%
93.4
1.0
0.4
0.3
2.1
1.1
0.4
0.3
0.4
0.5
Total
535,015
100
Source: Table L9101.7 Forward linkage rates
between 1991 and 2001 Censuses
Table 5 – Ethnic group at 2001 by sex and age
0-15
White
Mixed
Black Caribbean
Black African
Black Other
Indian
Pakistani
Bangladeshi
Chinese
Other
MALE
16-59
47,496 138,743
1,616
1,434
474
1,287
582
1,194
179
239
1,112
4,063
1,191
2,642
427
943
203
755
517
1,659
TOTAL
53,797 152,959
Source: ONS Longitudinal Study
FEMALE
16-59
60+
0-15
60+
48,576
136
476
121
29
928
467
187
129
218
45,762 143,312
1,584
1,610
453
1,658
502
1,490
157
302
1,097
4,456
1,122
2,653
464
1,165
181
817
463
1,748
63,083
162
490
104
20
832
275
91
129
175
51,267 258,023
51,785 159,211
65,361 276,357
Table 6 – Ethnic group by NSSEC at 2001 (16-59 year
olds)
NSSEC at 2001
Higher
Lower Prof Intermed Employers
Own
Man & Prof & Higher Tech
in small orgs Account
White
Mixed
Black Caribbean
Black African
Black Other
Indian
Pakistani
Bangladeshi
Chinese
Other
Lower tech
& super
Semi Routine Never worked
FT
routine
& l-t u/e students
27,790
288
207
245
33
986
280
68
188
359
65,075
561
666
454
110
1,155
426
120
231
576
34,180
323
433
234
55
794
288
88
99
263
7,941
53
41
45
5
446
224
115
159
133
14,964
101
89
58
18
422
321
21
73
113
26,148
187
227
137
36
486
229
119
54
194
42,938
396
442
399
90
1,230
657
360
186
462
34,146
277
315
196
60
1,239
713
239
77
290
9,038
273
207
354
45
713
1,531
742
102
472
19,805
584
316
562
89
1,048
625
236
403
545
TOTAL
30,444
Source:ONS Longitudinal Study
69,374
36,757
9,162
16,180
27,817
47,160
37,552
13,477
24,213
Table 7 – Ethnic group by Economic activity at 2001
(16-59 year olds)
Economic Activity at 2001
Employed Employed
Self- Seeking Retired Student Looking Perm sick
FT
PT employed
work
after home
White
Mixed
Black Caribbean
Black African
Indian
Pakistani
Bangladeshi
Chinese
Other
Other
138,874
1,142
1,400
968
3,471
1,204
292
505
1,250
39,497
280
310
233
860
404
273
130
315
26,102
199
149
134
975
494
125
236
279
9,768
204
217
236
391
388
165
44
182
4,071
11
30
17
89
30
11
20
23
20,265
613
335
610
1,081
660
248
408
585
21,156
276
201
234
743
1,219
599
135
411
14,396
135
164
84
442
322
108
27
117
7,896
183
137
168
467
573
287
67
245
TOTAL
149,106
Source: ONS Longitudinal Study
42,302
28,693
11,595
4,302
24,805
24,974
15,795
10,023
Table 8 – Ethnic groups by Government Office
Regions at 2001 (all people)
North
East
White
Mixed
Black Caribbean
Black African
Black Other
Indian
Pakistani
Bangladeshi
Chinese
Other
Government Office Regions at 2001
North Yorkshire
East West East of London South South Wales
West & Humber Midlands Midlands England
East West
25,344 65,084
153
607
11
172
35
139
4
62
136
803
142 1,447
62
336
42
222
77
306
48,421
478
241
96
44
617
1,755
165
141
214
40,612 48,748 52,757
468
693 548
220
785 246
75
108 128
30
90
37
1,578 2,457 667
339 1,777 501
106
399 232
160
171 252
210
396 292
48,216 78,597 50,334 28,859
2,157 850 389 199
2,785 222 130
26
3,060 247
68
37
574
54
25
6
4,858 1,094 185
93
1,474 747
66 102
1,677 178
43
79
706 328 130
62
2,467 586 149
83
TOTAL
26,006 69,178
Source: ONS Longitudinal Study
52,172
43,798 55,624 55,660 67,974 82,903 51,519 29,546
Table 9 – Ethnic group by religion at 2001 (all)
White
Black
Asian
Other
Religion 2001
Christian Buddhist Hindu Jewish
Muslim
Sikh
Other No religion Not stated
372,022
8,727
1,857
1,860
545
28
176
737
67
33
6,097
55
2,549
12
32
39
2,077
1,166
13,494
849
72
4
4,495
43
1,149
66
239
47
72,119
1,469
773
1,734
36,372
1,416
1,440
520
Total
384,466 1,486
Source: ONS Longitudinal Study
6,252
2,632
17,586
4,614
1,501
76,095
39,748
Imputation in the 1991 Census
• Edit & Imputation method
• Edit matrices
• Hotdeck method
• Not flagged in the LS
• Data imputed for wholly absent households
“Editing and imputing data for the 1991 Census”
I.Mills & A.Teague Pop Trends Summer 1991pp30-37
Imputation in the 2001 Census
• Edit & Donor Imputation System (EDIS)
• Edit
• Imputation
• One Number Census
“Census 2001 Review & Evaluation
Edit and Imputation: Evaluation Report” 2003
Table 10 – Imputation rates in the 2001
Census and the LS
2001 census
LS
Population Imputation rate Population Imputation
000's
%
%
49,359
0.56
539,879
49,359
0.44
539,879
49,359
0.32
539,879
49,359
1.30
539,879
48,848
1.70
538,026
48,848
2.91
538,026
48,848
1.09
538,026
48,848
1.42
538,026
48,848
3.92
538,026
48,848
4.53
538,026
35,367
391,841
35,367
391,841
35,367
6.09
391,841
35,367
3.69
391,841
33,686
6.14
369,784
33,686
9.15
369,784
33,686
3.34
369,784
21,741
3.48
244,104
29,335
13.81
369,784
369,784
28,065
4.73
304,380
Age
Sex
Marital status
Student flag
Country of birth
Ethnic group
Health
Carer
Long-term illness
Address one year ago
Educational qualifications
Professional qualifications
Highest qualification
Activity last week
Employment status
Workplace size
Supervisor
Occupation - currently working
Occupation - ever worked
Economic activity
Relationship to Person 1
Source:
2001 Census data from
"Census 2001 Review & Evaluation - Edit and imputation: Evaluation Report"
ONS Longitudinal Study
rate
0.20
0.40
0.24
1.24
1.65
2.80
1.02
1.34
3.83
4.45
6.05
6.05
6.05
3.63
5.72
8.85
3.25
3.29
4.33
9.41
4.62
Table 10A – Imputation rates for Ethnic
groups
ALL PEOPLE
WHITE
White British
White Irish
Other White
MIXED
White & Black Caribbean
White & Black African
White & Asian
Other Mixed
BLACK OR BLACK BRITISH
Black Caribbean
Black African
Other Black
ASIAN OR ASIAN BRITISH
Indian
Pakistani
Bangladeshi
Other Asian
CHINESE OR OTHER ETHNIC GROUP
Chinese
Other Ethnic group
Source: ONS Longitudinal Study
%
2.8
2.6
2.9
4.0
5.4
3.0
3.5
3.6
4.4
5.2
4.0
3.0
4.8
4.1
4.1
2.5
2.9
Table 10B - Relationships
IMPUTATION RATES
RELATIONSHIPS
Person relationship
Family relationship
Household relationship
Source: ONS Longitudinal Study
N
529,874
529,874
529,874
%
8.47
10.37
11.39
Table 11 – Imputation rates for a derived
variable
All people aged 16 to 74 ever worked
SOCIAL CLASS
Variable Imputation rate
%
SOC2000
OCCP0
4.33
Employment status
EMTP0
5.72
Supervisor status
SUMP0
3.25
Size of establishment
SIZP0
8.85
Social class
Source: ONS Longitudinal Study
11.00
Imputation and analysis
• Analysis with imputed values
• Analysis without imputed values in the dataset
• Analysis without imputed values in the variables
of interest
Table 12 – The effects of imputation
Ethnic group by marital status (16-74 year olds,
ever worked)
Marital status (16-74 year olds, ever worked)
Single
Married/
Sep/Wdwd/
Remarried Divorced
INDIAN
With imputed values
LESS
1659
54
6426
162
725
25
1605
187
6264
692
700
101
1418
5572
599
1521
61
1277
33
709
42
Without imputed values
1460
LESS
status
232
Without imputed values
1228
for economic activity
Source: ONS Longitudinal Study
1244
667
189
1055
131
536
Without imputed values
LESS
status
Without imputed values
for economic activity
BLACK CARIBBEAN
With imputed values
LESS
Change in ethnic group
• Consideration of change in ethnic group is
important for understanding the composition of
groups over time
• Almost 1 in 4 people recorded as Black African or
Black Caribbean in the 1991 Census reported a
different ethnicity in 2001, compared with less
than 1 in 10 South Asian and Chinese people,
and less than 1 in 200 White people
• Change in individuals’ reported ethnic group
between the 1991 and 2001 Censuses reflected
the introduction of new response categories in
2001, especially for mixed ethnicities
Per cent of people in selected 1991 ethnic
groups reporting the same group in 2001
100
99.5
91.0
80
77.2
60
Per cent
40
20
8.3
0
White
Indian
Black Caribbean
1991 ethnic group
Black Other
2001 ethnicity reported by people in the
1991 Other Black group
Other Mixed
5%
Other ethnic
groups
7%
White
15%
Mixed White &
Asian
2%
Mixed White &
Black African
6%
Black Caribbean
21%
Mixed White &
Black Caribbean
33%
Black African
3%
Other Black
8%
Loss to follow-up
• Loss between two censuses without valid exit
(death or embarkation)
• Caused by:
– Unobserved embarkation
– Census underenumeration
– Linkage failure (mismatched records)
• Higher rates of loss to follow-up among minority
ethnic groups
– 16 per cent of 1991 Black Africans expected in 2001
were not found
Follow-up of the 1991 traced LS sample by ethnic group
White
78.7
Black Caribbean
11.7
65.0
Black African
6.2
59.3
28.9
3.5
Black Other
37.2
71.7
Indian
1.6
77.3
Pakistani
3.1
69.4
Chinese
Other
10
20
Present in 01
30
28.4
6.1
30.2
71.4
0
28.5
4.3
63.7
3.1
40
50
60
Died or embarked 91-01
18.6
25.9
2.1
67.3
Other Asian
26.8
4.1
71.0
Bangladeshi
9.7
70
25.4
80
Not present in 01
90
100
Summary
• Small sample sizes may constrain ethnic group
analysis
• Need to consider how to treat 2001 item
imputation
• Change in ethnic group between 1991 and 2001
should also be considered
• Loss to follow-up is higher among minority ethnic
groups
– Potential for bias
– Impact on sample sizes when measuring transitions