Fig 3 Incidence rate ratios (IRR) for exposed versus unexposed by site of CT scan and type of cancer, based on a one year lag period. IRRs were calculated after stratification for age, sex, and year of birth. Heterogeneity between cancer types, by site of CT scan exposure: all sites, χ²=23.58 (6 df), P=0.001; brain, χ²=104.1 (6 df), P<0.001; abdomen or pelvis, χ²=15.7 (6 df), P=0.02. Heterogeneity between sites of CT scan exposure, by cancer type: all cancers, χ²=111.1 (6 df), P<0.001; brain, χ²=13.9 (6 df), P=0.03; leukaemia, χ²=24.81 (6 df), P<0.001