In reply: Hocking states that electromagnetic fields cannot be ruled out as a cause of childhood leukaemia. However, several large studies have all failed to find any association between childhood exposure to electromagnetic radiation and leukaemia.1-4 The two pooled meta-analyses Hocking refers to both found no increased incidence of leukaemia with exposure to electromagnetic fields of < 0.4 microtesla.5,6 Although there was an increased risk of leukaemia with exposure to ≥ 0.4 microtesla, 99.2% of children with leukaemia had not received such a high level of exposure. 5 In addition, both studies acknowledged the potential for selection bias. As such, for the overwhelming majority of children with leukaemia, exposure to electromagnetic fields does not play any significant causative role. Although we agree its effect cannot be ruled out for the remaining < 1% of patients, it should not be given undue epidemiological weight.
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