Postcodes as useful markers of social class: population based study in 26 000 British householdsCommentary: Socioeconomic position should be measured accurately
BMJ 1999; 318 doi: https://doi.org/10.1136/bmj.318.7187.843 (Published 27 March 1999) Cite this as: BMJ 1999;318:843
Postcodes as useful markers of social class: population based study in 26 000 British households
- John Danesh, Merton College junior research fellow (john.danesh@balliol.ox.ac.uk)a,
- Simon Gault, assistant statisticianb,
- Jo Semmence, statisticianb,
- Paul Appleby, research officerc,
- Richard Peto, professor of medical statistics and epidemiologya
- aClinical Trial Service Unit and Epidemiological Studies Unit, University of Oxford, Radcliffe Infirmary, Oxford OX2 6HE
- bFamily Resources Survey, Department of Social Security, London WC2N 6HT
- cImperial Cancer Research Fund Cancer Epidemiology Unit, Radcliffe Infirmary, Oxford OX2 6HE
- Department of Social Medicine, University of Bristol, Bristol BS8 2PR
- Correspondence: Dr Danesh
- Accepted 4 December 1998
Markers of poverty or of low social class are associated with many diseases and potential causes of disease, but medical studies often fail to record sufficient information on socioeconomic status.1 Postcodes of individuals are, however, often available in Britain, and commercial software exists that estimates household income from the postcode alone. We assessed how informative postcode income estimates are, either about reported household income or about other characteristics related to social class in a large, population based survey of British residents.
Methods and results
The family resources survey involves personal interviews with members of private households in England, Scotland, and Wales selected by stratified clustered probability sample.2 During 1995-6, 26 445 (70%) of 37 712 eligible households gave answers to questions on socioeconomic characteristics. Reported weekly household income was taken as the sum of all sources of pretaxation income (excluding housing benefit) reported by household members. During 1985 to 1993 members of 11 million households, or about half of all households in Britain, provided information to a marketing company about annual income and gave a complete address that included a full postcode—that is, 6 or 7 characters.
This information was used to produce commercial software that estimates household incomes from postcodes. After adjustments for regional variation and for inflation in reported income levels, the pretaxation incomes of at least six households were used to calculate a weighted average income for that postcode. When there were fewer than six responses, the income information was combined with the data for respondents with neighbouring postcodes until a reliable estimate could be made. Parts of this database are updated annually. We compared household income estimates obtained by FIND (a …