Mapping access to food in a deprived area: the development of price and availability indices

Objective: To develop and map indices to illustrate variation in the cost and availability of healthy food. Design: Two contiguous wards in London were selected by virtue of their high Carstairs deprivation scores. A 2-km area was defined around a randomly chosen central point. All retail outlets selling food within the area were visited and their location recorded. A list of foods, acceptable to the local ethnically diverse population, which met current dietary guidelines, was devised. Data on the availability and price of 71 food items were collected. Indices were developed using SPSS and mapped using Geographic Information System (GIS) software. Results: Information on availability and prices were collected from 199 outlets. The mean price index shows how expensive a shop is relative to other shops in the area. The least cost index shows the relative expense of a shop using the cheapest ways of buying their range of foods. Shorthand indices were tested, using data on 19 of the 71 prices. Availability indices are also discussed, including a green availability index and a fresh green availability index. Illustrative maps of the shop locations and the mean price index and fresh green availability index are shown. Conclusions: Data can be collected and indices developed which indicate geographic variation in shop 'expensiveness', and in the price and availability of healthy food. GIS software can be used to map these indices, to identify areas with high food prices or low availability.