2001 UK Census ONS 'imputing' information

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Our reference        FOI001376

Dear ms Woods,

In response to your request under the Freedom of Information Act, I write
to advise that the strategy adopted in the 2001 Census was that, in order
to meet the requirements of users for a complete and consistent set of
census results that represented the whole population, the enumerated
counts were adjusted to take account of:

(a)        missed data items that related to persons recorded in the
census;
(b)        the numbers and characteristics of persons missed in resident
households that were recorded in the census; and
(c)        the number and characteristics of persons in households that
were missed in the census.

Such adjusted data took account of information collected in a separate
Census Coverage Survey, and by comparing these with the data collected in
the Census itself. The methods of imputation used to derive the adjusted
data adopted standard statistical methodology which had been shown to
provide accurate estimates. The underlying methodology has been published
on the ONS website at:
[1]http://www.ons.gov.uk/ons/guide-method/c...

The value of the resulting statistics are thus much enhanced in comparison
with outputs where ‘not stated’ counts are included. As a result, all
users were able to analyse the same results and draw similar or comparable
conclusions. This had not been possible in previous censuses when users
themselves had to estimate the numbers and characteristics of people and
households not enumerated

The application of different levels of imputation, with the aim of
improving the utility of the statistics, is now adopted by many countries
conducting field enumeration censuses, and is, as far as England and Wales
is concerned, provided for by the provisions of the Census Act 1920 under
which the Census is lawfully carried out.

Details of the level of item imputation and record imputation in the 2001
Census (from which the Daily Telegraph may have obtained their figures)
were published in 2001 Census of England and Wales Quality Report in 2005.
This reported that the proportion of people missed in the Census was
estimated to be six per cent, comprising four per cent in  households that
were enumerated and two per cent in households that were missed. The same
report also recorded that some six per cent of households were imputed.

The quality report also describes the particular method of imputation
adopted. A copy of this is available from our website at
[2]http://www.ons.gov.uk/ons/guide-method/c...

Imputation has been carried out only by members of ONS staff.

All personal data provided in the census is kept secure for 100 years. It
is unlawful, under the provisions of the Statistics and Registration
Service Act 2007 for ONS, or anyone employed by ONS, to disclose any
personal census information.

You have the right to have this response to your freedom of information
request reviewed internally by an internal review process and, if you
remain unhappy with the decision, by the Information Commissioner. If you
would like to have the decision reviewed please write to Dennis Roberts,
Office for National Statistics, Room 1214, Government Buildings, Cardiff
Road, Newport, Gwent, NP10 8XG.

If you have any queries about this email, please contact the Freedom of
Information Team ('[email address]')

Please remember to quote the reference number above in any future
communications.

Freedom of Information Team
Office for National Statistics

For the latest data on the economy and society consult National Statistics
at http://www.ons.gov.uk

 

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Legal Disclaimer : Any views expressed by the sender of this message are
not necessarily those of the Office for National Statistics

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References

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1. http://www.ons.gov.uk/ons/guide-method/c...
2. http://www.ons.gov.uk/ons/guide-method/c...