Does your measure matter? A comparison of alcohol availability measures in Great Britain

Introduction The relationship between the spatial availability of alcohol and alcohol-related harm is well established; however the specific components of availability which drive this relationship and how availability may best be measured remains unclear. This study applies a range of alternative measures of availability to selected areas in Great Britain to establish to what extent they are related to each other. Methods Using a database giving low-level geographic location (full postcode) and type e.g. (bar, supermarket) of every licensed outlet selling alcohol across 4 times points (2003, 07, 10, 14) we calculated low-level measures of alcohol availability for three Local Authorities covering a spectrum of population density and deprivation. Measures were calculated based proximity, outlet density, outlet clustering and so-called ‘gravity’ measures. The relationships between measures are explored descriptively and through correlation and factor analysis. Results The availability of alcohol is high in the selected Local Authorities, with an average of 45 outlets within 1km of any individual postcode and a mean distance of 400m to an on-trade and 900m to an off-trade outlet. Different measures display different temporal trends with the density and gravity measures having close agreement with each other while proximity measures suggest different trends. Socioeconomic patterning varies both between Local Authorities and measures chosen, with similar agreement between density and gravity measures and different patterns displayed for proximity measures. Conclusions These findings highlight that different measures applied to different geographies may give fundamentally different characterisations of availability. The choice of availability measure used in any study does, therefore, matter and should not be made without appropriate regard to theoretical considerations