EWCPOP - SOCPOP - MIGPOP
1991 census output with allowances for undercount

Estimating with confidence: Ian Diamond, Ludi Simpson, Rachel Crossey
Quantifying the Impact of Census Undercount: Ludi Simpson, Liz Middleton
Census data adjusted for undercount

The 1991 Census achieved a 98% coverage - an extremely good result compared to any survey enquiry, and similar to other developed countries with a tradition of census collection.

However, the 2% missed - ‘the missing million’ - were concentrated among children, young adults and the very elderly, and in the most urban areas of Britain. The average undercount among male adults in all city Districts of Britain was much higher, at 20%. There were also some special cases - such as the considerable undercount of armed forces at some bases.

Using plausible differentials of undercount between areas and between social groups, backed by consistent evidence from the UK and other countries, three sets of new population estimates have been estimated and are widely used in central and local government, health authorities, and within academic research.

Many applications of the census are unaffected by the census undercount, but in all cases the question should be asked:

"Could the level of undercount in the 1991 Census affect the conclusions of this study?"

Some studies have been shown to be particularly affected if the census counts as published are used in place of estimated full population counts, for example:

• Net migration flows between areas of Britain
• Net requirement for housing or jobs
• Population estimates
• Age-sex composition, in particular when the size of the young adult population is important

The datasets incorporate Crown Copyright data. They were created within two ESRC-funded projects by the following teams: Estimating with Confidence (Ian Diamond, Ludi Simpson, Rachel Cossey) and Quantifying the impact of census undercount (Ludi Simpson and Liz Middleton).

Publications:

Ludi Simpson and Liz Middleton (1999) "Undercount of migration in the UK 1991 Census and its impact on counterurbanisation and population projections," International Journal of Population Geography, 5: 387-405.

Stephen Simpson and Danny Dorling (1994) "Those missing millions: implications for social statistics of non-response to the 1991 Census," Social Policy 23, 543-67.

Stephen Ludi Simpson, editor (1998), A one number census: proceedings of a research workshop. Manchester: CCSR occasional paper 15 University of Manchester.

Contact: Ludi Simpson