Rebasing the annual mid-year population estimates for England and Wales

The ONS produces mid-year population estimates annually, which are based on updating from the most recent census. Therefore, whenever results become available from a census, a new base is created for the population estimates. This has implications for historic series, which need to be revised to be consistent with both the past and the most recent census. This article describes the methodology that will be used for this rebasing of the mid-year population estimates following the availability of results from the 2001 Census. Census results also provide a unique opportunity to assess the accuracy of the population estimates that are based on the previous census and this article also describes the approach that will be taken to the assessment of accuracy.     

The 2007 Census Test: evaluation of key objectives

The Office for National Statistics conducted a major census field test in May and June 2007 as part of the planning and preparation for the next census of population and housing in England and Wales in 2011. The 2007 Census Test was a large scale test covering approximately 100,000 household in five local authorities (LAs) selected to reflect a range of geographic conditions and social characteristics. Within England the Test covered parts of Bath and North East Somerset, Camden, Liverpool and Stoke on Trent. In Wales the Test took place in Carmarthenshire. The selected LAs were chosen to provide a varied cross section of the population and types of housing that would be covered in a full census. This article summarises the evaluation results and, where decided, decisions for 2011 on four key aspects of the Test: delivery method - post-out compared with hand delivery; inclusion of an income question; outsourcing recruitment, training and pay; and liaison with LAs.     

A cross country review of the validation and/or adjustment of census data

This article reviews existing procedures employed by various countries in the evaluation of, and/or adjustment, either of census data, or of population estimates based upon census data. The work was carried out to ensure all potential demographic techniques are considered by the ONS for the post census evaluation process of the 2011 Census.     

2011 census coverage assessment and adjustment strategy

Every effort is made to ensure everyone is counted in a census. However, no census is perfect and some people are missed. This underenumeration does not usually occur uniformly across all geographical areas or across other sub-groups of the population such as age and sex groups. Coverage levels in censuses across the world are declining leading to an increasing need to firstly slow the decline through improved enumeration, and secondly in improved methods and data for measuring coverage. In order to achieve the mission critical aims of the 2011 Census, a coverage assessment and adjustment strategy is required. This article outlines the proposed strategy for the 2011 UK Census. The strategy is to significantly improve upon the 2001 One Number Census, and use it as a platform to develop an improved coverage assessment and adjustment methodology. The article also outlines the key areas of innovation for the 2011 strategy and the options that will be considered in order to develop the final strategy. Stakeholder management is also an important part of the strategy to ensure that key users both buy into and understand the methodology. ONS will look to build on the consultation carried out prior to the 2001 Census and widen the user base with which it engages on this important topic.     

Quality assuring the 2011 Census population estimates

The 2011 Census is a once in a decade opportunity to gain an accurate picture of the population. Quality assurance of the census population estimates is vital to ensure data robustness and that users have confidence in the results. This article provides a detailed summary of the methods being used to achieve this quality assurance, including the processes and adjustments.     

Developments in census taking in the last 25 years

This article looks back at censuses of population conducted since 1971. It identifies some of the most important changes with respect to questions asked, methods of collecting the census and the production of outputs. In particular it discusses the introduction of the ONS Longitudinal Study following the 1971 Census and the Samples of Anonymised Records following the 1991 Census. This article outlines some of the changes being introduced for the 2001 Census, including methods of dealing with under-enumeration and improved access to outputs.     

The 2007 Census Test: a major step towards the 2011 Census

The Office for National Statistics (ONS) is planning a major Census field test in 2007. It will form part of the planning and testing programme leading to up the next Census of Population for England and Wales in 2011, which will also include a Rehearsal in 2009. The 2007 Test will be a large-scale test in five local authority (LA) areas selected to reflect a range of field conditions, covering some 100,000 households in total. Within England the Test will cover parts of Bath and North East Somerset, Camden, Liverpool and Stoke-on-Trent. In Wales the Test will take place in Carmarthenshire. The selected LAs have been chosen to provide a varied cross-section of the population and types of housing that would be covered in a full census. This article sets out the main aims for the Test and describes the design and location of the sampled areas and the basis for their selection. It goes on to detail the ways (previously reported in Population Trend 1251) in which the ONS Census team and the LAs involved are working in partnership in planning the census enumeration with the long-term view of improving overall census coverage and user confidence in the results. The article notes that decisions on the topics to be covered in the 2007 Test have only recently been decided, and concludes with an overview of the qustions to be included in the 2007 Test questionnaire.     

2011 Census Field design: getting the numbers right

A labour force of over 30,000 temporary field staff has been employed to carry out the Census. This article summarises the role of the field staff in collecting census questionnaires from households and communal establishments for the March 2011 enumeration. Building on the lessons learned from the 2001 Census, and taking account of changes in society and technology since 2001, the article provides a summary of the planned field staff structures and processes intended to deal with returned questionnaires and non-responders.     

Covering all bases: early thoughts for population bases for the 2011 Census

This article discusses early thinking on the options for the population bases to be used in the 2011 Census. It describes some of the work being conducted to enable a decision about bases to be reached, including historic and international reviews of censuses. It also discusses the implications that our rapidly changing society has for census planning.     

The Census Coverage Survey--the key element of a one number census

The key measure of census quality is the level of response achieved. In recent censuses worldwide this level has been in the high nineties per cent. This was also true of censuses in Britain in 1991 (98 per cent). However, what was particularly noticeable about the census in Britain in 1991 was the differential response rate and the difficulty in effectively measuring this. The One Number Census programme was set up in the UK to research and develop a more effective methodology to measure and account for underenumeration in the 2001 Census. The key element in this process is the Census Coverage Survey--a significantly larger and redesigned post-enumeration survey. This article describes the planning and design of the survey with particular emphasis on the implementation of the proposed field methodology in practice. It also provides a high-level overview of the success of the survey.     

Population estimates; backseries methodology for 1992-2000

In each decade, population estimates are rebased using data from the most recent census. However, this would lead to a step change in the population estimates series. To avoid this discontinuity the backseries for 1992 to 2000, was revised to bring it into line with the 2001 Census. This article discusses the methodology used to produce the final revised backseries for 1992 to 2000 published by ONS in October 2004. The final estimates were produced after a long period of research into the best methodology to use. Traditionally, the backseries have been revised using an interim simple period method, followed by a final simple cohort method. The approach taken following the 2001 Census was much more comprehensive. This article outlines this approach, summarises the range of methods available and describes in detail the final method selected.     

Introducing the area classification of output areas

This article provides a brief introduction to the Area Classification of Output Areas. The classification uses data from the 2001 Census to group the 223,060 output areas into groups of similarity based on their census attributes. The classification is freely available as a 'National Statistic' via the National Statistics website.     

An analysis of patient register data in the Longitudinal Study - what does it tell us about the quality of the data?

This article uses data for members of the ONS Longitudinal Study (LS) from both Census 2001 enumeration and patient registrations "frozen" on census day 2001 from the National Health Service Central Register (NHSCR) to examine potential sources of difference in area of usual residence.Overall 95.7 per cent of ONS LS members enumerated at census resided in the same area as recorded on the NHSCR data. Where areas differed, or the ONS LS member was not on the NHSCR on census day, subsequent NHSCR records were examined. Records flagged on the NHSCR as ONS LS members in England and Wales on census day but with no census record were also investigated.     

The 2011 Census: a proposed design for England and Wales

This article sets out the proposed design for a 2011 Census in England and Wales, as part of the ONS's proposed future population statistics system. The design draws on experiences from the 2001 Census and changes in available technology, and takes account of the many comments received from respondents to a Discussion Paper published in October 2003 and of views expressed at a joint ONS/RSS Conference on 11-12 November 2003. The article highlights the statistical and operational strategic aims for the 2011 Census, the major changes proposed from the 2001 approach, and gives an indication of the benefits and risks. It is important to note that this design remains a proposal at present, the elements of which will be subject to further research building on comments received during consultation and a detailed testing programme over the coming years.     

Key issues in the quality assurance of the One Number Census

As part of the 2001 Census, the One Number Census project estimated and adjusted the Census database for underenumeration. As a result of the highly innovative One Number Census and the Quality Assurance process it encompassed, it was also ensured that robust results could be obtained for each local authority area. This article examines some of the issues and analyses that were undertaken as part of that assessment of the 2001 Census population counts for England and Wales. The article firstly highlights the key issues surrounding the implementation of the 2001 Census fieldwork. The article then explores the 2001 Census results through a series of demographic analyses to illustrate the sorts of issues investigated during the One Number Census Quality Assurance process itself. These analyses look at the patterns contained within the results, and comparisons with key alternative sources of population counts. Overall, these in-depth analyses and investigations provide further credence to the plausibility of the One Number Census results.     

Change in living arrangements following death of a partner in England and Wales, 1971 to 2001

Understanding trends and changes in the circumstances of couples separated by death is important for policy initiatives to reduce vulnerabilities associated with end of life care and for those who live on. This article uses widow(er)hood statistics and census data from the Office for National Statistics Longitudinal Study. It examines changes in couples' living arrangements and households at four successive censuses from 1971 to 2001 and shows how these differ by age and gender on the death of a spouse or partner. Findings draw attention to the effects of ageing and mortality improvements as well as wider social and economic trends in family and household formation, residential independence in older age, and policy developments on long-term care provision for older people.     

The long shadow of childhood: associations between parental social class and own social class, educational attainment and timing of first birth; results from the ONS Longitudinal Study

In September 2004, linked data from the 2001 Census was made available in the Office for National Statistics (ONS) Longitudinal Study (a 1 per cent sample of the population of England and Wales). The study now includes information from four censuses on sample members and the people they lived with. The availability of this new information, the length of follow-up and other features of the study (such as records of births and deaths to sample members) provide new opportunities for analysing change--both over the life course, between time periods, and between generations. This article illustrates the potential for analysis of continuity and change with new results on intergenerational social mobility, and on parental social class and age at first birth.     

Interim 2001-based national population projections for the United Kingdom and constituent countries

This article describes new 2001-based national population projections which were carried out following the publication in September 2002 of the first results of the 2001 Census. These "interim" projections, carried out by the Government Actuary in consultation with the Registrars General, take preliminary account of the results of the Census which showed that the base population used in previous projections was overestimated. The interim projections also incorporate a reduced assumption of net international migration to the United Kingdom, informed by the first results of the 2001 Census and taking account of more recent migration information. The population of the United Kingdom is now projected to increase from an estimated 58.8 million in 2001 to reach 63.2 million by 2026. The projected population at 2026 is about 1.8 million (2.8 per cent) lower than in the previous (2000-based) projections.     

Fifty years of United Kingdom national population projections: how accurate have they been?

This article considers the accuracy of the official national population projections made for the UK over the last fifty years The findings take account of the revision to population estimates following the 2001 Census and are largely similar to the findings of a previous review carried out after the 1991 Census. The total population has been projected reasonably accurately but this is largely a chance result of compensating errors in the assumptions of fertility, mortality and net migration. The largest differences between projected and actual populations are for the very young and the very old, while projections of the working age population have been comparatively accurate. Fertility and mortality errors have reduced in more recent projections, while migration errors have grown. However, this may simply reflect the volatility or stability of the respective time-series at the time the projections are made. Changes in estimates of the past and current size of the population (highlighted by the revisions made to population estimates following the 2001 Census) are also shown to play a part in explaining projection error.     

Population bases and the 2011 Census

In an increasingly complex society there are a number of different population definitions that can be relevant for users, beyond the standard definition used in counting the population. This article describes the enumeration base for the 2011 Census and how alternative population outputs may be produced. It provides a background as to how the questions on the questionnaire were decided upon and how population bases can be constructed from the Census. Similarities and differences between the information collected across the three UK Censuses (England and Wales, Scotland and Northern Ireland) are discussed. Finally, issues around estimating the population on alternative bases are presented.