Townsend deprivation index
The Townsend deprivation index is named after Prof Peter Townsend and was first proposed in Townsend et al. (1987). It is a simple census-based index of material deprivation calculated by the combination of four census variables and has seen extremely widespread use. The Townsend index is an area-based measure and can be constructed for any geographical area for which census data are available, with extensive use of 1981, 1991 and 2001 censuses throughout the UK, most usually calculated for wards, enumeration districts (EDs) and output areas (OAs). A comparable measure can be constructed in other countries where the same census variables are available. It has served both as a general measure of deprivation for academic studies of health care need, educational achievement and crime and also as an input to various resource allocation mechanisms intended to target resources to areas of greatest social need. The simple nature of the score and its use of readily-available data mean that it can be calculated directly for any geographical areas based on census geography. Geographical linkage may then be required in order to allocate deprivation scores to records referenced to incompatible geographies such as postcodes.
The index is constructed from the following four census variables, each of which must be divided by the appropriate count of households or persons to obtain a percentage score. The exact census counts to be used will vary slightly for different censuses.
- Households without a car
- Overcrowded households
- Households not owner-occupied
- Persons unemployed
The unemployment and overcrowding percentages (+1) are then subjected to a log transformation in order to normalise the raw values, which tend to be highly skewed. All four variables are then standardized using a Z-score (subtract the mean value and divide by the standard deviation). These four standardized scores are then summed to obtain a single value which is the Townsend deprivation index. Positive values of the index will indicate areas with high material deprivation, whereas those with negative values will indicate relative affluence. A score of 0 represents an area with overall mean values.
When calculating Townsend scores, it is necessary to know the mean and standard deviation for each variable for the appropriate geographical units across a large reference area - typically the whole country. The score can be standardized over smaller areas, such as a region, but this will not produce nationally comparable values.
Paul Norman, formerly of the Centre for Census and Survey Research at the University of Manchester has calculated Townsend scores for 2001 census wards and his scores and notes on the method used are available for download at http://cdu.census.ac.uk/related/deprivation.htm
Senior, M. (2002) Deprivation indicators. In: Rees, P., Martin, D. and Williamson, P. (eds) The Census Data System Wiley: Chichester, pp. 123-137
Townsend P, Phillimore P, Beattie A. (1988) Health and Deprivation: Inequality and the North Croom Helm: London