LETTER: How the 1991 population figures were calculated

From Mr P. J. Wormald Sir: The headline on your article on the 1991 census ("Census figures abandoned after 2 million are missed", 23 December) misrepresents the quality of census outputs. Overall response to the census was 97.5 per cent compared with 98per cent in 1981. This was comparable to best international standards.

The suggestion that the census figures have been abandoned is complete nonsense. The census is the largest data set available on the social condition of the population. It provides invaluable information for small areas to enable key planning decisions to be made. We have published more than 400 volumes of results for local areas and for particular topics. These are far and away the best figures of their kind.

As well as publishing results on the census, we take seriously our duty to inform users of the quality of the statistics. We first published details of the census undercount in October 1992 and have published further details at regular intervals. Most r ecently, we have published the Census Validation Survey, which contains very detailed information on the quality of census outputs.

A key use of the census is to update population estimates at national and local level. But in producing population estimates, the Office of Population and Census Surveys (OPCS) draws on other sources of information as well as on the census. For 1991, ouranalysis indicated that there were particular deficiencies in the census counts for men aged 20-30. Other sources were accordingly used to supplement the census information for this group in particular.

Details of the adjustments made to produce population estimates were published in various OPCS publications and the procedures were quality assured by an eminent external adviser, Professor Ian Diamond of Southampton University, who has publicly said that he is completely satisfied with them. The final estimates have been in the public domain and accepted for the last year and a half.

I do accept the need to find ways of improving the quality of future censuses. This is a major task on which we are already embarked. Various studies have been carried out and we are working closely with the British Society for Population Studies and theRoyal Statistical Society in organising an open conference on this subject in April. Subsequently, there will be full consultation on any proposals we bring forward for changes to the way censuses are conducted.

Yours faithfully, P. J. WORMALD Director and Registrar General Office of Population Censuses and Surveys London, WC2

23 December