The accuracy of general practitioner records of smoking and alcohol use: comparison with patient questionnaires

Background General practitioner (GP) records are increasingly being used as sources of information on potential confounders such as smoking use and al cohol intake in epidemiological studies. The aim of this study was to asses s the accuracy of GP records on smoking use and alcohol intake compared wit h data from patient questionnaires. Methods Patients registered with 42 practices in Oxfordshire that agreed to take part in a post-marketing surveillance study of omeprazole were sent a postal questionnaire that included questions about alcohol and tobacco use . Two years later, data on these aspects of lifestyle were abstracted from the GP records. Results A total of 892 patients agreed to take part in the study; 804 (90 p er cent) completed the postal questionnaire, and the records of 856 (96 per cent) were reviewed. Information on smoking and alcohol use was present in 74 per cent and 63 per cent of GP records, respectively. Agreement between the two data sources was moderate for both smoking (kappa = 0.50) and alco hol use (kappa = 0.52). With regard to smoking, the main discrepancy betwee n the two data sources was that 46 per cent (94/206) of patients who report ed themselves as ex-smokers were recorded as being never smokers in the GP record. With regard to alcohol, there were no systematic differences betwee n the two data sources. Conclusion Data from GP records on smoking status and alcohol use are incom plete and subject to some misclassification. This is a source of potential failed adjustment for confounding, which should be considered in epidemiolo gical studies that make use of these records.