Census: Under-Enumeration of Males aged 20–44 (Hansard, 5 December 2002)

The information requested falls within the responsibility of the National Statistician who has been asked to reply.

Letter from the National Statistician, Len Cook, dated 5 December 2002.

As National Statistician and Registrar General for England and Wales I have been asked to reply to your recent question asking whether Her Majesty's Government are concerned about the apparent under-enumeration in the 2001 Census among males aged 20–44. [HL310]

For the 2001 Census a new and more robust method was used, known as the One Number Census. In addition to the Census itself, a huge independent coverage survey was undertaken, covering around 0.32 million households and every local authority (the Census Coverage Survey). This survey was then combined with the Census, using standard statistical techniques, to estimate the Census non-response and to adjust for under-enumeration. There was also an extensive Quality Assurance process for every local authority, comparing the Census results with a range of other administrative data; and a national Quality Assurance process resulting in additional adjustments.

This approach was adopted because we knew that Census non-response had been increasing internationally and that response to the 2001 Census was likely to be lower than previously. It is the use of this robust method, adjusting under-enumeration, which gives me confidence that the Census figures provide the most accurate possible estimate of the population.

For men aged 20–44, the response rate to the Census in England and Wales was 90 per cent. That is based on the final estimates derived from both the Census and the Census Coverage Survey, thus indicating that the One Number Census method added 865,000 males aged 20–44 to the estimate that would have been obtained by the Census alone. The response rate varied within that age-range as follows: 87 per cent for men 20–24, 88 per cent for men aged 25–29, 90 per cent for men aged 30–34, 92 per cent for men aged 35–39, 94 per cent for men aged 40–44. These and further details about response were published with the Census results on 30 September and are available on the National Statistics website at http://www.statistics.gov.uk/ census2001/annexb.asp.

The 2001 Census results showed that the United Kingdom has 800,000 fewer men aged 20–44 than previously thought. The critical factor within the difference appears to be emigration. The data used to estimate the numbers of people leaving the country is derived, from the International Passenger Survey (IPS). This works well, but it captures travellers' intentions at the time of departure. These may be prone to change once people are abroad, particularly among young men with few ties at home. These issues are currently under consideration as part of the 131WA National Statistics Quality Review on International Migration, and one of the outcomes expected of this review is a set of options to improve intercensal population estimates, which will particularly involve males 20 to 44.