The Carstairs index is an index of deprivation used in spatial epidemiology to identify Socio-economic confounding. The index was developed by Vera Carstairs and , and published in 1991 as Deprivation and Health in Scotland. The work focusses on Scotland, and was an alternative to the Townsend Index of deprivation to avoid the use of households as denominators. The Carstairs index is based on four Census variables: low social class, lack of car ownership, overcrowding and male unemployment and the overall index reflects the material deprivation of an area, in relation to the rest of Scotland. Carstairs indices are calculated at the postcode sector level, with average population sizes of approximately 5,000 persons.