From Introduction: In its review of the possible health effects of extremely low frequency (ELF) magnetic fields, the expert scientific Working Group assembled by the International Agency for Research on Cancer (IARC) concluded that high levels of magnetic fields were associated with childhood leukemia, but it could not exclude the possibility “that a combination of selection bias, some degree of confounding and chance could explain the results” (IARC, 2002). An IARC press release called attention to a 0.4-μT^Footnote1 exposure value stating, “pooled analyses of data from a number of well-conducted studies show a fairly consistent statistical association between childhood leukaemia and power-frequency residential magnetic field strengths above 0.4 microTesla” (IARC, 2001). The Working Group based its conclusion largely on pooled analyses by Ahlbom et al. (2000) and Greenland et al. (2000) that combined data from selected individual epidemiology studies. These pooled analyses reported an association with childhood leukemia at magnetic field intensities greater than 0.3 and 0.4 μT, respectively, using <0.1 μT as the reference level. No association was reported between childhood leukemia and magnetic field intensities below 0.3 or 0.4 μT, respectively.