Unit 1: A 'Quick' Introduction to the Census by w93zRS


									A "Quick" Introduction to the Census

Welcome to the on-line resources introducing you to the census!

After you've finished this unit, you should be able to:

      Outline the nature and contents of the 2001 and 1991 Census
      Discuss some potential uses of Census data
      Consider the limitations of Census data when doing research
      Undertake a simple, practical analysis of Census data relating to mode of travel to
       work and/or household characteristics (e.g., occupations and ethnicity).

Content Author: Dr. Myles Gould, School of Geography, University of Leeds and Richard
Wiseman, Mimas, University of Manchester
Developers: Linda See, Helen Durham and Andy Nelson (Richard Wiseman, redeveloped
and updated in 2009)

1 Introduction

Official statistics in the UK are collected by the Office for National Statistics (ONS), General
Register Office for Scotland, and Northern Ireland Statistics and Research Agency (NISRA).
ONS provides consistent national and local information about the UK population, housing,
employment, education and health care needs to Central Government, Local Authorities,
Health Authorities as well as a range of other users.

Before examining the Census in more detail, let's consider the more general topic of
secondary data sources.

Secondary data

      routinely collected and presented on some regular basis (every 10 years in the case of
       the census)
      collected for a particular (primary) purpose and are subsequently made available for
       other additional (secondary) purposes

When using secondary data, there are a number of questions that should be asked, including:
    How are the data collected?
    How are they classified/measured?
    What is the data quality and coverage?
    What is the data availability?
During the course of this tutorial we will consider each of these issues in relation to the

Test your knowledge
Census data are collected by:
   □ OECD
   □ ONS
   □ BBC
   □ The Home Office
   □ Local Authorities

2 What is the Census?

The national Census involves the total enumeration of the population (i.e. a complete head
count) at a single point in time. In the UK every householder is legally required to complete a
census questionnaire. For this reason, the Census is unique in that it provides national
coverage and near complete enumeration of the population (Dale and Marsh, 1993).

A Census has been undertaken every ten years in England and Wales since 1801. The only
exception was in 1941 due to the Second World War.

Stop for a moment and think about the following questions:

      Where were you during the last Census (29 April 2001)?
      Were you living in a house or a 'communal establishment'?
      Did you fill out a Census form or did someone else in your household do this?
      If you saw the form, do you remember any of the questions?
      Did you ever wonder what the Census was being used for?

Let's consider the answers to the last two questions in more detail…

Test your Knowledge
The national census involves:
   □ A 1% longitudinal survey of the population with continuous data linkage and update
       of lifestyle and behavioural characteristics
   □ A very incomplete enumeration of the population
   □ A 50% random survey of the population
   □ An 80% random survey of the population
   □ An attempted total enumeration of the population

2.1 What Census Questions are Asked?

The Census includes key demographic details such as age and sex, information on ethnicity,
religion, occupation and socio-economic class, and also details on household accommodation
and amenities (Dale, 1993a).

Data are also collected on car ownership, mode of travel to work and educational
qualifications. The box below summarises the questions asked in either the 1991 and 2001
Source: based on Martin (1991).

Test your knowledge
Which of the following topics are NOT included in either the 1991 and 2001 Censuses?
  □ Employment
  □ Age
  □ Sex
  □ Housing tenure
  □ Income

Test your knowledge
What does the word 'decennial' mean?
  □ A census that contains 10 different sets of geographical units.
  □ A census that contains 10 groups of tables.
  □ A census that is organised for a country that is sub-divided into 10 geostatistical
  □ A census that is undertaken every 10 years.
  □ A census that classifies the whole population into 10 occupational classes.

2.2 Uses of Census Information

Once the data are collected and processed (a mammoth task in itself!), it is possible to use
Census data to:

      Describe the demography of an area. For example, Census data are used extensively
       by Local Authorities and Health Authorities to develop profiles of their localities to
       inform their understanding of local demography and service needs, as well as aid
       decisions about facility planning. Census data are also used by Central Government
       for resource allocation to Local Authorities and Health Authorities.
      Explore the nature of relationships between demographic and socio-economic
       variables, such as housing tenure, amenities and occupational status.
      Calculate statistical rates such as death or unemployment by using Census data as a
       denominator with other sources of data.
      Combine census variables into a single overall index or measure of deprivation
       (Townsend et al., 1988; Senior, 1991). Also see unit: Measuring and Explaining
       Deprivation for more information.

Please note that the Census cannot be used to identify individuals. The Office for National
Statistics has strict guidelines to maintain confidentiality.

In the practical exercises at the end of this tutorial, you will get some hands-on experience
with using Census data. Hopefully this will give you an idea of the types of real world things
we can do with the data!

Test your Knowledge
Which of the following is NOT a possible use of the census?
  □ Calculating a rate.
  □ Identifying individuals for receiving additional social security benefits.
  □ Exploring relationships between different variables.
  □ Producing deprivation indices for allocating government resources to local areas.
  □ Describing the demography of a ward.

2.3 Geographical Data Structure
Census data are aggregated and made available for a number of geographical areas in the
2001 census. For confidentiality reasons some datasets are only available at certain
geographical levels. In addition, there are differences between the countries.
Output Areas are the base units of the 2001 census data releases. In previous censuses,
Enumeration Districts (EDs) were used both for data collection and output. However, EDs
were used in the 2001 census, but only for data collection only.

You can learn more about census geography by visiting the Census geography section within
the ONS Beginner's Guide to Geography.

2.4 Outputs

Census data are made available as published reports, covering different geographical regions.
A series of national and county reports and monitors are published that provide detailed
tables and key statistics. For the 2001 Census these outputs are available via the relevant
agency website:

      England and Wales
      Scotland
      Northern Ireland

In addition, you should find copies of printed reports for the 2001 and earlier censuses in
most libraries. If you want to do any "proper" analysis with the Census, you need to be able
to access the data in an electronic form. (See the unit: Accessing Census Data Using

2.5 Topics in the Census Aggregate Statistics

The 2001 Census contains a very large number of tables covering a range of different topics.

Popular topics include age, ethnic group, religion, accommodation type, and socio economic

An overview of the 2001 Census topics is available from ONS.

The census adapts each decade, questions on topics of new significance are added, while
others are omitted. The ONS Census Topics 1801-2001 leaflet illustrates this change.

2.6 CAS Dataset Types

2001 Census

A number of datasets were made available for the 2001 census. These are described below.

Key Statistics
Key Statistics provide a picture for any area of interest. The Key Statistics have been
designed to enable easy comparison between areas across the full range of Census variables.
The Key Statistics tables are the most easily comparable across the 4 countries.

Standard Tables
The Standard Tables (ST) provide the most statistically detailed view of the Census data.
They have been designed to present a wide range of cross-tabulated Census results in terms
of topics and geographical areas. They are not produced for small areas.

Standard Table Theme Tables
The Standard Tables Theme Tables are designed to contain information about ranges of
subjects related to particular themes, combined in single tables for ease of reference. They are
not produced for small areas. Themes covered include 'Older People', 'Ethnicity', 'Students
and Schoolchildren' and 'Religion'.

Census Area Statistics (CAS)
The CAS have been designed as reduced versions of the Standard Tables, though available at
all geographic levels right down to Output Area. Like Standard tables they have been
designed to present a range of cross tabulated results. Tables in the CAS cover topics such as
'Sex and Age by Economic Activity', 'Age by Highest Level of Qualification' and 'Type of
Accommodation by Tenure, Whether Furnished and Central Heating' for example.

CAS Theme Tables
Theme tables are available that combine a range subjects about a given theme: 'Dependent
Children', 'All People', 'Ethnic Group' and 'Ethnic Group of Households Reference Person'.
Like all CAS tables these are available at all geographical levels down to Output Area.

CAS Univariate Tables
The Univariate Tables provide a more detailed view on a single variable. Tables available
include 'Cars or Vans', 'Number of People Living in Households', 'Occupation' and 'Provision
of Unpaid Care'. if you are after simple statistics at the most detailed level of geography then
Univariate tables are a very good source of data. Like all CAS tables these are available at all
geographical levels down to Output Area

Armed Forces Tables
The Armed Forces tables provide information on members of the Armed Forces. These tables
are produced for local authorities (UV and District) and higher geographies only in England
and Wales. Armed Forces tables and variables are prefixed with the letters AF in Casweb.

1991 Census

The information and statistical 'counts' available in the 1991 CAS vary depending upon
whether you access data using the SAS (Small Area Statistics) or the LBS (Local Base
Statistics). Data are also for other geographical units including standard regions, counties,
local authority districts, health authorities, old regional health authorities and postcode areas.

The key things to note about these two 'interrelated tiers' of computer readable data are (Cole,

      The SAS are available for the most finely grained geographical areas, i.e.
       Enumeration Districts
      The LBS has more detailed information than the SAS
      The LBS has 13 more tables than the SAS
      The LBS has more than twice as many different items of information ('counts') for
       geographical areas than the SAS, which has only 9,000
      Some items of information are duplicated both within and between the LBS and SAS
      Any duplicated item of information for any particular geographical area (i.e
       ward/OAs or district/postcode sectors) found in different LBS tables, or discovered in
       both the LBS and SAS, will always vary slightly due to data modification (also
       known as data blurring) undertaken to protect against individual confidentiality.

2.7 Other Census Outputs

There are a number of other census-related products available. These include:

      Interaction data involve flows of individuals in the UK between origins and
       destinations. These flows are either the residential migrations of individuals from one
       place of usual residence to another or of commuters making journeys from home to
       workplace. Interaction data is available through the Centre for Interaction Data
       Estimation and Research (CIDER)
      digital boundary data for wards, Output Areas and other geographical areas, which
       can be used to display census data in map form (Barr, 1993). More information is
       available at UK Borders
      the Sample of Anonymised Records (SARs), which contain non-identifiable census
       responses for samples of individuals and households and provides a valuable source
       of 'microdata' (Marsh, 1993a).
      The England and Wales Longitudinal Survey (LS), has followed a 1% sample of the
       population who share one of four dates of birth since the 1971 Census. New births and
       immigrants who share these birth dates are also added to the LS database. Potential
       academic users (i.e. those working or studying in the UK Higher Education sectors)
       should initially approach the CeLSIUS team: Centre for Longitudinal Study
       Information and User Support (CeLSIUS). A similar Longitudinal Survey has been
       established for Scotland by the Longitudinal Studies Centre - Scotland (LSCS) and
       Northern Ireland by the Northern Ireland Longitudinal Study (NILS)

Up to now we've had an overview of the Census and the types of available outputs. Now we
move on to discussing the limitations of using census data…

2.8 How do I Access Census Data?

Unrestricted use of the main 2001 Census data has been granted by the three Census
agencies, but for publication and re-use a licence is required. The Census data remains Crown
copyright, however the Government has offered to waive normal copyright restrictions in
order to encourage widespread use of the material. To take advantage of this offer any
organisation wishing to publish or re-use the data should obtain a Click-Use Licence:

This licence can be freely obtained, please refer to the following sites for further information:

As long as you are studying or researching in an UK University or College, you can access
Census data for the 2001, 1991, 1981 and 1971 census using:

      Casweb
2001 Census data can also be accessed via:

      Neighbourhood Statistics (online access to England and Wales data)
      SCROL - Scotland’s Census Results Online (online access to Scottish data)
      NISRA Access to Northern Ireland Census results.
      Nomis UK labour market statistics from official sources.

3 Six Caveats

   1. Census data go out of date quickly - Decennial population censuses only provide a
      snapshot of the UK population every ten years. Data for areas that have experienced
      rapid population change will be particularly unrepresentative and will need to be
      supplemented with data from other sources.
   2. People missing from the Census - It was estimated that there were 1 million people
      not enumerated in the 1991 Census mainly accounted for by a shortfall in the number
      of men aged 19-31 (Marsh, 1993b, p.157). For males in their twenties the shortfall
      was over 20% for all city and Inner London districts (Heady et al., 1994). The 2001
      Census is considered the most accurate count of the UK ever achieved. This was
      achieved through a strategy known as the 'One Number Census'. This involved a
      follow-up survey Census Coverage Survey. See the ONS Quality of Results page for
      more details
   3. Census data are subject to other inaccuracies - These are due to transcription and
      coding errors (Wiggins, 1993). Overall, the accuracy and completeness of national
      censuses is, however, felt to be very good.
   4. Problems with comparison - It is difficult to make meaningful comparisons between
      different populations, geographical areas or time periods without knowledge of the
      underlying population being considered. Information about whether study populations
      are similar in terms of their size and composition should be compared. Rates are used
      to adjust/control for differences in the size of populations amongst the areas or sub-
      groups being compared.
   5. Census data are aggregated - Individual data are added up and combined together
      into a number of areas or geographical units for publication. These statistical data
      outputs are subject to the 'ecological fallacy' - the problem of inferring individual
      characteristics from group data (Openshaw, 1984). However, census microdata based
      on anonymised individual records are available in the SARs.
   6. Disclosure control - In the 2001 Census, a number of measures were applied to
      prevent the inadvertent disclosure of information about identifiable individuals. These
      measures included small cell adjustment, record swapping and the introduction of
      thresholds. See the ONS Disclosure Protection Measures page for further information

Test your Knowledge
When are census data most useful and meaningful?
  □ As soon as they are published and made available to users.
  □ On the night of the census.
  □ 6 years after they are published.
  □ 9 years after they are made available.
  □ They are only useful if you are interested in studying the distribution of income.
4 Population Estimates and Projections

In the previous page, we mentioned that the Census only provides a 'snapshot' of the
population every ten years. However, for many purposes it is important to have regularly
updated population estimates.

The term population estimate are estimates of the population between Censuses. They are
based on initial information from a census, together with what is known about births, deaths
and migration patterns from the NHS Central Register (Fox, 1990) .

The Office of National Statistics produces national and sub-national population estimates in
paper as Series PP1: Mid-Year Population Estimate. Electronic data are also available in the
UK Data Archive. Many Local Authorities in England and Wales produce ward based
population estimates (Simpson, 1998; Simpson, et al., 1997). The accuracy of the estimates
and projections will depend upon the methodology used and also the quality of the data used.

Here is a very simplified outline of the methods used to produce population estimates:

   1. Take the baseline population data from the Census.
   2. Deduct the number of deaths known to have occurred during the year(s) under
   3. Add the number of births.
   4. Add the number of immigrants.
   5. Make adjustments for the age distribution.

5 Conclusions

This learning resource has provided you with a quick overview of the nature, structure and
potential uses of the Census. If you have found this resource interesting and useful, you might
want to visit other census related web sites or follow up some of the suggested reading. In
particular you might want to look at some of the other on-line resources offered on this site.

What follows now are some practical exercises on the use of the Census illustrated
through two different scenarios.

6 Practical Exercises

The following exercises are based around two different 'work based' scenarios and provide
practice in using census data. Scenario #1 requires you to look at a number of maps showing
different census variables, interpret what you see, suggest some 'policy' recommendations and
reflect on your answers. Scenario #2 involves using tabular data, making some simple
calculations, shading in a map, analysing this and suggesting other sources of data to support
your answers. You can learn more about how to map, visualise and analyse data in other

The data relates to the 'wards' that make up the Leeds local authority district. The statistical
extracts and information contained in this worksheet were obtained from The 2001 Census,
Crown Copyright (ESRC purchase).You may not reproduce any of the abstracts, maps, data
and information in this handout without the permission of the Census Office in England.
General Instructions

   1. The scenarios are available in a number of formats. Please select the required file (as
      directed by your teacher - if appropriate) from the list below.
   2. Complete all appropriate tasks and answer all appropriate questions (as directed by
      your teacher - if appropriate) associated with the scenario. Your teacher will tell you
      if you need to hand in answers, and if so, how you should write up and submit your
   3. You will require a ruler, pencil and eraser if you complete the activity involving
      shading in the map (scenario #2, task 4).
   4. You will require a pocket calculator, pen/pencil and eraser to complete some of all the
      tasks if you intend printing out the exercises/resources now and then do not intend
      using a computer further. Your Windows desktop has a calculator in Accessories.
      Alternatively, use Excel.

Scenario 1

You are a self-employed environmental research consultant with some additional skills in
'computer mapping' and some knowledge of transport planning issues. You have been
commissioned to write a report on local transport patterns, environmental pollution, and
health status in Leeds. You have been provided with some 2001 Census data relating to levels
of car ownership and mode of transport used to travel to work.

As a starting point you decide to map this data and describe and comment upon the patterns
shown, and make some policy recommendations. The maps are provided as Figures 1-9. You
can also take a look at a map of Leeds containing the ward names.

      Figure 1
      Figure 2
      Figure 3
      Figure 4
      Figure 5
      Figure 6
      Figure 7
      Figure 8
      Figure 9

   1. Briefly describe the mapped patterns, commenting on areas that might be expected to
      have particularly high levels of car utilisation and pollution levels.
   2. Suggest area based transport initiatives for increasing public transport use within the
      Leeds district. In addition, suggest possible areas (and routes - see hint below) that
      might benefit from ''environmentally friendly'' transport schemes' and might help
      reduce the prevalence of respiratory illness. Give the reasoning behind your answers.
      Hint: If you would like to suggest routes, try and refer to a map or street atlas of
      roads in Leeds, if you can put your hands on one. Ask in your University/College
      library, or a public library, or use the Web - see Multimap, Streetmap or Google
   3. Re-assess your answers to questions 1. and 2. and give reasons why they might be
      problematic and misplaced.
   4. What other information and sources of primary and secondary data might you
      consider using in preparing your consultancy report?

Scenario 2

You are employed by Leeds City Council and are working on a project to reduce domestic
fuel consumption, increase recycling and promote energy saving. Your section has the
ambitious task of trying to devise an advertising campaign and educational programme to
increase public awareness of environmental issues and change individual behaviours. You are
under pressure from both the Councillors and Chief Executive to score an early success! You
decide to target particular neighbourhoods to increase awareness. The departmental 'data
analyst' has gone on leave. They have left some half-prepared data from the 2001 Census.
You decide to brave it and look at the data!

Note: You will need some files to complete this practical. Click on the links below to open
the files directly or right click to save them to your hard disk:

      Table 1 in comma separated format
      Table 2 in comma separated format
      These questions are also available in rtf format
      a base map of Leeds in .rtf format
      Map of Leeds containing ward names

Use the electronic version of the questions if you wish to fill in the answers electronically and
then print them out for submission. Bring the base map into your word processing package
and print it off as you will shade this map by hand.

Tasks/Questions for Scenario 2

   1. Bring Table 1 into a spreadsheet package and fill in the 'blanks' by calculating the
      appropriate percentages.
   2. What are the maximum and minimum values for % HRPs in Higher and intermediate
      managerial/administrative/professional classes, and also % HRPs in semi-skilled and
      unskilled manual workers and which areas are these?
   3. Complete Table 2 in your spreadsheet package by calculating the 'average' for the
      percentage of people who rent from a local authority or housing association; and also
      the percentage of people who are owner occupiers (buying or outright). Fill in the
      blanks and show your calculations.
   4. Using the data from Table 2 and the Leeds base map, which you need to print out
      first, construct a choropleth map of "% 2 or more cars or vans in household". Select 5
      class intervals, and using a pencil, devise 5 shading styles. Indicate these styles by
      marking them in the legend provided on your map, and also note your chosen class
      intervals. Now shade all the area which fall in each of the class intervals in turn.

       Hint: look at the maps in Scenario 1 if you need some ideas about what is required
       and also use the Leeds wards map to find the areas.

   5. Using Tables 1 and 2, your map and your answers to the previous questions (where
      appropriate) make suggestions and comments about:
         o Which areas you might target (with your campaign) to maximise impact.
       o  Which areas might require added effort and resources to ensure you get your
          message across.
       o Explain your rationale and thinking behind these suggestions.
6. What additional data and information might you seek to qualify your answers if you
   were not so pushed for time and had added extra resources? How might you go about
   obtaining this?

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