Methods and basic data of case-control study of leukaemia and lymphoma among young people near Sellafield nuclear plant in West Cumbria.

To examine whether the observed excess of childhood leukaemia and lymphoma near the Sellafield nuclear plant is associated with established risk factors or with factors related to the plant. A case-control study. West Cumbria health district. 52 Cases of leukaemia, 22 of non-Hodgkin's lymphoma, and 23 of Hodgkin's disease occurring in people born in the area and diagnosed there in 1950-85 under the age of 25 and 1001 controls matched for sex and date of birth taken from the same birth registers as the cases. Antenatal abdominal x ray examinations, viral infections, habit factors, proximity to and employment characteristics of parents at Sellafield. Ascertainment of cases through multiple sources was as complete as possible, and the diagnosis was established for nearly all cases from hospital records and by independent pathological review when suitable material (60% (58) of cases) was available. Identification and tracing of the parents of cases and controls enabled questionnaires to be forwarded to 730 (66%), and 467 (64%) of the questionnaires were returned completed. Obstetric records were located for 481 (44%) of the relevant births, more frequently in recent years. Linkage of study subjects to the Sellafield workforce file enabled dates of employment and records on external doses of whole body ionising radiation to be obtained. Concordance of information from duplicate sources (when available) was reasonably high with no indications of bias. Overall the collected data were sufficiently reliable for detailed analysis and careful interpretation.