Introduction
Learning objectives: You will learn about demographic data and census data in greater detail.
Please read the resource text below.
Resource text
Demographic data
As examples of collections of population level demographic data, we will consider the national census and the General Practice-based Exeter database.
Census data
The most important source of demographic data at the population level for the UK is the ten-yearly census.
Description
Within the United Kingdom, the national population is determined on the basis of the national census. Modern censuses have their origins in western Europe. There are still many countries where there have been no censuses or ones covering only urban populations, or only conducted after several decades. Countries such as the Netherlands and Germany have population registers, where each person is required to register with the local authority when they move house and these countries have abandoned undertaking censuses.
In Great Britain, a census has been carried out every ten years since 1801, except for 1941[1]. It attempts to count all people and households on one day. The census is overseen by the Office for National Statistics. Before 2001, to administer the census, areas were organised into Enumeration Districts (EDs) of approximately 200 households. In 2001, EDs were replaced by Output Areas, which use areas covered by postcodes as the building blocks. Output areas have approximately 125 households on average, and a minimum of 40.
2011 may be the last UK census, as one proposal is to launch a population register.
Method of a census
A census form is delivered to every household and residential establishment in the country. The forms are completed by members of the household, officially by the 'head' of the household, referring to the specified date of the census, and returned by post. Participation is a statutory requirement, and enumerators follow up any households from which no form is returned. In 2001 the data requested related to normal place of residence; in previous decades data was requested for location on the night of the census. Face-to-face interviews are carried out with a large sample, over 300,000, of households, to check coverage and estimate under-enumeration (numbers of households and persons missed by the census).
Data collected
Data is collected on individuals and on households. The exact data set varies from census to census. Ethnicity data were first collected in 1991, and the ethnic group classifications were changed for the 2001 census. Areas currently collected include the following.
For individuals:
- demography: age, sex, ethnic group, country of birth, religion, marital status, population mobility. In 2011 the expectation is that nationality will be added.
- health: general health status, limiting long term disability, provision of unpaid care
- social class and occupation: economic activity status, occupation, industry. From these, socio-economic classifications are developed. In 2011 the expectation is that income will be added.
- education: level of qualifications achieved.
For households:
- household size and structure
- number of rooms
- type of tenure
- amenities
- lowest floor level access
- access to a car or van
- method of transport to work.
Methods of administration in Scotland and Northern Ireland differ from England and Wales. Responsibility lies with the General Register Office for Scotland and the Northern Ireland Statistics and Research Agency.
How results are analysed
Households are aggregated into postcodes, the key constituent unit. Each residential postcode includes about 17 households. Reference files produced by collaboration between the Royal Mail, Ordnance Survey, and ONS link postcode to geographical coordinates, and to each larger physical and administrative structure (current or past) of which they are a part. Up to 1991 the basic census aggregate unit for analysis was the Enumeration District (ED), the caseload for a single enumerator, but problems were experienced regarding unevenness of size. In 2001 these were supplanted by a new category, the Output Area (OA). These are roughly 125 households, and as compact and homogenous as can be derived, where possible following natural and administrative boundaries. These, in turn, may be aggregated for analysis and publishing purposes into Super Output Areas (SOA), comprising one or more Output Area. Data is analysed by means of cross-tabulations of census variables at OA level, which can be aggregated to SOA, Electoral Ward, Local Authority level etc. all the way to the entire country. OAs have the advantage over the old EDs (Enumeration Districts) that they are based on Census Geography and designed to be helpful to the analysis of the census, whereas EDs were based on an administrative geography, designed to be helpful for splitting the work of enumeration officers.
How the results are disseminated
Large datasets containing 'key statistics' for the whole country are available from ONS on CD-ROMs on request. Small area data is available on-line from the ONS and Neighbourhood Statistics websites. Access may also be provided via some academic websites, though these may only be accessible to a limited range of users. There is also a computer analysis suite, SASPAC, which includes both complete small area statistical data and software for analysis and presentation. Look-up tables from OAs to higher units, and OA and urban & settlement boundary files for use in geographical information systems are available on CD or DVD from ONS, generally without charge.
Issues of confidentiality
Data supplied on census returns are considered absolutely confidential. No form of analysis or presentation is performed or permitted that would enable any individual to be identified, either directly from census data or when census data is viewed in combination with other available sources of data. ONS operates a strict policy of disclosure protection that applies to successive unit aggregates. As a general rule, any cell containing fewer than six persons must either be suppressed or combined with another small cell. This issue can be the factor that determines which geographical level is chosen for release of data.
Uses
- resource allocation.
- health, educational, transport and housing planning.
- the denominator for health and other population statistics.
- analyses of population trends on a wide range of areas: for example health, illness.
- describing deprivation: Townsend, Jarman and Carstairs deprivation scores are all Census based. The index of multiple deprivation (IMD2004) assigns a deprivation score to each super output area (SOA) and local authority in England[2]. SOAs are made up of groups of output areas. IMD2004 uses Census data to estimate population denominators.
Strengths
- it is the most complete source of information about the population because it aims to include everyone.
- the results of the census are considered the nearest there can be to a gold standard national population.
- data is collected at one time.
Weaknesses
- expensive (2001 Census cost approximately £250 million[3]).
- criticisms of the Census include a tendency to undercount children, young men, homeless people, and members of the armed forces. In 1991, it was estimated that 10% of men in their 20s and 8% of people over 85 were missed. In 2001, most of the criticisms related to possible undercounting of inner city populations.
- only undertaken every 10 years.
- self reporting - accuracy difficult to assess. The elderly tend to overstate their age or round to the nearest five years, divorced men tend to report that they are single.
- ethnicity not added until 2001.
- the data can take a long time to be released.
- take care when interpreting results, especially at small area level when the data will not be so robust.
There may be systematic bias in the census process. In 1991 the enumeration omitted all homeless people. In 2001 the count of young men was substantially lower than expected, which may relate to a cohort who wished to be unknown for tax registration reasons. Members of the armed forces may be omitted. Some questions may be intentionally mis-answered: in the mid 20th century there was concern about deliberate misreporting of age by women, and in 2001 there was an unsuccessful, nation-wide campaign to get the fictitious Jedi Knights recognised by the census as a religion.
Exeter data
Another example of a source of demographic data in England, is the Exeter database, managed by the National Strategic Tracing Service.
Description
The Exeter database stores information at individual patient level, on patient registration with general practitioners. It contains information on:
- NHS Number
- name
- address
- postcode
- sex
- date of birth
- place of birth
- GP and GP Practice patient is registered with
- PCT of where the patient is registered
Uses
- the main purpose of the Exeter system was to pay GPs, on the basis of list capitation.
- for tracing people as they move and register with a new GP.
- for providing GPs with a register.
- deprivation of registered patients at ward level is also factored in when calculating primary care resource allocation.
- for recording national adult cancer screening programmes data.
- for understanding local populations and to inform practice based commissioning.
Strengths
Crucial for practice profiling by practice clusters, PCTs and public health observatories.
Postcodes enable determination of local authority of residence. Local authorities do not have equivalent databases of their residents, and in collaborative work between NHS and LAs, the picture of the population that Exeter makes available can be enormously useful.
Weaknesses
GP lists are inflated on average by 5.7%, due to mobility among young adults and delays in removing list members after death or emigration.
Vulnerable populations such as homeless people, asylum seekers, travellers, and some migrant workers tend not to be registered with GPs so are missing from the Exeter system.
Place of birth, which might be useful in ethnic analyses, is a free text field, and may vary from 'home' to country to detailed address.
This covers factors such as age, sex, migration patterns, ethnicity, marital status in populations and how it influences health.