In 2001, the Census results represent 100% of the population. Total overall response was 98 per cent. This includes some 4 per cent of the population estimated to be resident in households identified by enumerators. Census response, the proportion of people returning a form in England and Wales, was 94 per cent.
Following evaluation of the 1991 census a number of new initiatives were introduced to maximise coverage. These included encouraging people to post back their census forms to enable census staff to focus on those most likely to have difficulty filling in their forms, smaller workloads for staff in the more difficult areas, redesigned and carefully tested forms and questions, a community liaison programme including translation of census material into 26 languages, and a focused programme of awareness raising and publicity.
We knew, however, that we would not get complete coverage and indeed expected that undertaking the census would be more difficult in 2001 than it had been in 1991. The pattern of increasing difficulty of obtaining response to a census was also evident in many other countries.
In most census taking countries it is standard practice to measure the level of census under-enumeration by either a post enumeration survey and/or by comparison of aggregate census counts with aggregate data from other sources such as health registers or benefit records. It is usual practice to produce a report assessing the level of census response for the purpose of re-basing a population estimate series, but the results of the census itself have never been adjusted for under-enumeration.
For the first time, however, all the 2001 census results in the UK have been adjusted for estimated under-enumeration. That is, all tables from the census will account for the whole population.
Recognising the increased difficulties in conducting censuses in the UK, particularly those experienced in the 1991 census, the Office for National Statistics (ONS) and its fellow census offices in Scotland (GROS) and Northern Ireland (NISRA), adopted a new approach to the census in 2001. Rather than relying on a single enumeration, the strategic approach to the census in 2001 was to carry out a traditional census followed by a sample re-enumeration (the Census Coverage Survey).
The One Number Census
By combining the results of the two operations and using statistical methods, ONS has been able to derive census estimates representing 100 per cent of the population, that is as if the census had counted everyone. This is called a One Number Census and is a major step forward from previous UK censuses where users of the census results have had to make judgements as to whether the estimated level of under-enumeration affected the use that could be made of the results. In previous censuses, two population counts were published; one raw unadjusted census count, and a subsequent count including the estimated under-enumeration which formed the base for annual population estimates.
In 1991, the estimated coverage and total overall response of the census in England and Wales was 98 per cent. This was the proportion of the population accounted for in the census results. It included some 2 per cent estimated by enumerators to be resident in identified households but from whom no completed census form was collected. Thus census response in 1991, defined as the proportion of the population counted on returned census forms, was 96 per cent in England and Wales.
In 2001, coverage of the census in England and Wales was 100 per cent. Total overall response was 98 per cent. Using the same definition as for 1991 it is estimated that 98 per cent of the population in England and Wales was covered in 2001, the same as for 1991. This includes some 4 per cent of the population estimated to be resident in households identified by enumerators but from whom no completed census form was returned. Census response in 2001 for England and Wales is therefore estimated to be 94 per cent.
Corresponding census response and coverage rates for 1991 and 2001 for England and Wales separately are shown below, together with figures for England and Wales as a whole.
Components of UK Census response and coverage rates for 1991 and 2001 - England and Wales
England
Wales
England & Wales
1991
2001
1991
2001
1991
2001
A People on returned forms: Census Response Rate
96
94
97
94
96
94
B Other people in identified households
2
4
1
4
2
4
A+B Total overall response
98
98
98
98
98
98
C People not included on returned forms and people in wholly missed households
2
2
2
2
2
2
Total
100
100
100
100
100
100
Proportion of population covered in census results: Census Coverage Rate 1991: A+B 2001: A+B+C
98
100
98
100
98
100
Note: The 1991 rates shown are subject to slight change, but this does not affect the conclusions to be drawn from this analysis.
One of the main reasons that it was necessary to develop the One Number Census approach for the 2001 census is that under-enumeration does not occur uniformly across all age-sex groups. The patterns of census response were as expected, that is response rates were lowest for persons in their twenties, particularly men. 2001 census response by age-sex group for England and Wales as a whole varied from 98 per cent for females aged 75-79 to 87 per cent for males aged 20-24. Census response rates by age-sex group for both the 1991 and 2001 censuses are shown in an attached spreadsheet. These show that:
Census response has declined between 1991 and 2001 for most age-sex groups. This decline in response rates is in line with changes that have been observed for large-scale Government Surveys during the 1990s; response rates for censuses conducted in other countries have also fallen over the past decade, for example the level of under-enumeration observed in the censuses of both Australia and New Zealand rose between 1996 and 2001;
Census response is lowest for the 20-24 age group for both men and women - for men, this was also the case in 1991, but for women in 1991 the lowest census response was estimated to be for those aged 85+;
The largest difference in response rates is for Females 20-24 where response is 6 per cent lower in 2001 than 1991;
The response rate for children is much lower in 2001 than in 1991;
Response rates were higher in 1991 than 2001 for both men and women across all age groups except for those aged 80 and over;
In both 1991 and 2001 there was a significant drop in response rates for those aged between 20 and 30; and;
Generally there is a higher response rate for women than men, although this difference is smaller in 2001 than in 1991.
Figure 1: Census Response by Age & Sex - England & Wales
Under-enumeration in the 2001 census did not occur uniformly across all areas. The patterns of census response were as expected, that is response rates were lowest for inner city areas where characteristics known to be related to census non-response are most prevalent - multi-occupancy and higher proportions of non-English speaking population etc.
At a subnational level, it is only possible to compare response rates for 2001 and 1991 for broad categories of areas that were used in calculating the 1991 census under-enumeration rates. The 1991 census rates and the composition of these broad categories are contained in the 1991 Census Validation Survey: coverage report (HMSO, 1994). The table below shows the response rates for the area types. This indicates that 2001 census response was lower in all area categories, with broadly similar proportionate drops across all areas with the exception of Inner London and Outer London, which have higher decreases in response rates. Inner London had the lowest response rate in 1991 and has recorded the largest absolute drop in 2001.
Census Response by area - England & Wales
All people
Male
Female
1991
2001
1991
2001
1991
2001
Inner London
88%
78%
86%
77%
90%
79%
Outer London
96%
90%
95%
89%
96%
90%
Main Metropolitan areas
94%
92%
92%
91%
96%
92%
Other metropolitan areas
97%
95%
96%
95%
98%
96%
Non-metropolitan cities
95%
94%
93%
93%
96%
94%
Other non-metropolitan areas
97%
96%
97%
96%
98%
97%
Cardiff, Newport & Swansea
95%
93%
94%
93%
97%
94%
Other Welsh areas
97%
94%
97%
94%
98%
95%
Total
96%
94%
95%
93%
97%
94%
Note: The 1991 rates shown are subject to slight change, but this does not affect the conclusions to be drawn from this analysis.
The table below displays the census response rates for each of the Government Office Regions (GORs). It shows census response was highest in the South West, the East Midlands and the North East, and lowest in London. Within all of these regions, female response rates are higher than corresponding male rates and these differences were most significant in the North East, East Midlands, London and the South East.
Census Response by Government Office Region 2001
Government Office Region
All People
Male
Female
North East
96%
95%
97%
North West
94%
94%
95%
Yorkshire and The Humber
95%
95%
96%
East Midlands
96%
95%
97%
West Midlands
95%
95%
96%
East of England
95%
95%
96%
London
85%
84%
86%
South East
95%
94%
96%
South West
96%
96%
97%
Wales
94%
93%
94%
Across all local authorities, census response varied from 99 per cent for Teesdale to 72 per cent for Hackney, with the exception of one outlier, Kensington and Chelsea, where census response was 64 per cent. The table below presents the ten local authorities that had the highest response rate, and those ten that had the lowest across England and Wales. The ten highest local authorities all had response rates of 99 per cent in 2001 - in total there are 17 authorities that have over 99 per cent. All of the top 10 areas are all in non-metropolitan areas as defined by the 1991 census area classification. The 10 local authorities with the lowest response rates are all in Inner London. The results for Kensington and Chelsea and similar Inner London boroughs were subject to further quality checks.
Highest and lowest response rates by Local Authority 2001
Rank
Highest Response rates, 2001
Lowest response rates, 2001
1
Teesdale
99%
Kensington and Chelsea
64%
2
Castle Morpeth
99%
Hackney
72%
3
Selby
99%
City Of London
74%
4
South Norfolk
99%
Westminster - City of
74%
5
St. Edmundsbury
99%
Tower Hamlets
76%
6
Broadland
99%
Hammersmith and Fulham
76%
7
North Devon
99%
Camden
77%
8
Kennet
99%
Southwark
77%
9
Chester-le-Street
99%
Islington
78%
10
Alnwick
99%
Lambeth
79%
The chart below shows the distribution of response rates for the 376 local authorities in England and Wales. It shows a skewed distribution, and highlights that 92 per cent of response rates across the country were above 90 per cent, with over two thirds over 95 per cent. The attached spreadsheet displays the response rates for all local authorities in England and Wales, sorted alphabetically.
2001 Census Estimated Person Response rates by local authority and Hard to Count Group
For the 2001 Census each postcode was classified into one of three Hard to Count (HtC) levels, 1 being the easiest, and 3 the hardest. In addition, the population was divided into 37 age-sex groups. This means that there were 111 separate estimation strata in any given Estimation Area (EA). In some cases it was not possible to produce good quality estimates of these groups separately. In these cases groups were combined, referred to as 'collapsing strata'. [More details as to how this was applied...] (pdf file).
Each postcode in the CCS was used to represent undercount in a number of postcodes in the population. When an unusual observation occurred in a postcode it was likely that it was not representative of other postcodes. In order that the unusual postcode (referred to as an outlier) did not have an undue influence on the rest of the population, it was removed from the sample. Information pertaining to the methodology used to determine outliers together with the number of outliers identified within each local authority can be found within the individual local authority reports.
The tables provide, for each local authority, the estimated response rates for each Hard to Count group and the number of outliers. The ONC estimation process used pre-defined stratification. These were the Hard to Count (HtC) index and 37 five-year age-sex groups. The HtC index was based on 1991 Census data, and was used to draw the sample and to form estimation groups. Whilst this was the best stratification that could be used at the time, there may be areas where the Hard to Count index gave a poor stratification. Analyses have been undertaken to examine the change between the 1991 HtC distribution and that implied by the 2001 Census data. The results of these analyses can also be seen within the individual local authority reports.
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