Validation of smoking history in cancer patients.

OBJECTIVE: The aim of the study was to investigate the agreement between patient records and the information reported from relatives, and how the relationship and time since patient's death affected the response rate and the quality of the data. METHODS: A questionnaire regarding smoking history was sent to next-of-kin of 270 deceased women diagnosed with breast cancer during 1958-2000 in the Stockholm County. Agreement between the reports of next-of-kin and patient records was calculated using a kappa statistics, along with its 95% confidence interval. RESULTS: When information about overall smoking history from patient records and next-of-kin was compared, the kappa value was 0.83 (95% confidence interval (CI): 0.73-0.92). Using two smoking categories (15 cigarettes), for quantitative smoking history the kappa value was 0.46. No evidence of a trend toward under-/over-reporting among next-of-kin was found. The overall smoking agreement between medical record and next-of-kin was similar for the two median recall periods (10 years), with kappa value 0.80 and 0.83, respectively. CONCLUSION: Next-of-kin can provide reliable information with almost perfect agreement with patient records on lifetime smoking status, and should be considered in studies where information on smoking history is missing.