Tehran University of Medical Sciences Iranian Journal of Public Health 2251-6085 37 4 2008 12 15 26 31 M Movahedi Dept. of Epidemiology, School of Public Health, Shaheed Beheshti University of Medical Sciences, Te T Bishop Genetic Epidemiology Unit, Cancer Research UK, St.James Hospital, Beckett Street, LS9 7FT, Leeds, JH Barrett Genetic Epidemiology Unit, Cancer Research UK, St.James Hospital, Beckett Street, LS9 7FT, Leeds, GR Law Centre for Epidemiology and Biostatistics, University of Leeds, 30 Hyde Terrace, Leeds, LS2 9LN, UK 2015 10 03 Background: A crucial part of a case-control study is the selection of a sample of controls that represent the base-popula­tion from which cases were drawn. Controls may be matched to cases by one or more potentially important confounding vari­ables, such as socioeconomic status. In the United Kingdom, one method for control selection has been based on the pa­tient list of the General Practice with whom the cases were registered, which we refer to as GP-matching. We aimed to ex­plore whether GP-matching adequately control for the potential confounding effect of socioeconomic status. Methods: The Townsend index of deprivation was calculated for different two national census geography levels of Elec­toral ward/Postcode Sector and Enumeration District/Output area for the three study areas of Dundee, Leeds and York. Con­ditional logistic regression was used to estimate the association of cases with deprivation (based on the Townsend index) com­pared with that of matched controls for the two geographical scales. Results: At the largest geographical level (Electoral ward/Postcode Sector) there was no evidence of a difference in the dis­tribution of deprivation scores between cases and controls. However, analysis at the smallest level (Enumeration Dis­trict/Output area) showed that, despite GP matching, cases were more likely to live in deprived areas than matched controls.  Conclusion: Using General Practice lists for the selection of controls for controlling the confounding effect of socioeco­nomic status might not be an appropriate method for case-control studies conducted in the United Kingdom. https://ijph.tums.ac.ir/index.php/ijph/article/view/2010 https://ijph.tums.ac.ir/index.php/ijph/article/download/2010/1991