CCRG magnetic fields study

The CCRG study (also known as the "Draper" study) is a study conducted by the Childhood Cancer Research Group at the University of Oxford into childhood cancer rates around high-voltage power lines.

In 2005, the group published a paper in the British Medical Journal giving the results for proximity to power lines.  This found an elevated incidence of leukaemia within 600 m.  That paper noted that this was too far for it to be explainable by any magnetic-field effect, but it didn't give the actual magnetic-field calculations.

In September 2010, the same group published a new paper in the British Journal of Cancer.  See the full paper on the Journal's website.  They calculate the magnetic field from the power lines using historical information and present the results for magnetic fields directly.  They give the key results in Table 4 in the paper, reproduced here:

Diagnostic group Categorical analysis.  Reference level: <0.1 µT
Magnetic field (µT)
Continuous analysis
RR per 0.2 µT
0.1 to <0.2 0.2 to <0.4 >=0.4
Leukaemias 2.00 (0.50 to 7.99) 0 case/2 control 2.00 (0.18 to 22.04) 1.14 (0.57 to 2.32)
CNS/brain tumours 0.50 (0.09 to 2.73) 1 case/0 control 0.33 (0.03 to 3.20) 0.80 (0.43 to 1.51)
Other cancers 0.33 (0.07 to 1.65) 1.00 (0.14 to 7.10) 5.00 (0.58 to 42.80) 1.34 (0.84 to 2.15)

(The figures in the table are relative risks, with 95% confidence intervals in brackets.  If there are either no cases or no controls in a particular category, relative risks cannot be calculated.)

The authors say:

"Although not statistically significant, the estimate for childhood leukaemia resembles results of comparable studies."

This is referring principally to the Ahlbom pooled analysis.

They also say:

"Magnetic-field exposure during the year of birth is unlikely to be the whole cause of the association with distance from overhead power lines previously reported from this study."

This reinforces the message from the 2005 distance study.  It can be seen most clearly in a graph in the paper (redrawn here in colour):

The red (circles) shows the distance results - an elevation for childhood leukaemia.  The blue (diamonds) shows the estimated risk found for magnetic fields in each of these distance bands (assuming there is a magnetic field effects at all), calculated in slightly different ways for the first band and for the other two.  The two risk estimates are consistent in the first distance band, 0-50 m, but in the words of the paper:

"...within each of the distance bands 50 to <100m and 100 to <200 m, the mean RR prediction from estimated magnetic-field exposure is much smaller than the actual RR estimate found by the distance study. This argues against a magnetic-field explanation of the distance association in these bands ..."

The abstract of the paper is:

British Journal of Cancer (2010) 103, 1122 – 1127
Childhood cancer and magnetic fields from high-voltage power lines in England and Wales: a case–control study

ME Kroll1, J Swanson2, TJ Vincent1 and GJ Draper1
1University of Oxford, Childhood Cancer Research Group, Richards Building, Old Road Campus, Headington, Oxford OX3 7LG, UK; 2National Grid, 1-3 Strand, London WC2N 5EH, UK

BACKGROUND: Epidemiological evidence suggests chronic low-intensity extremely low-frequency magnetic-field exposure is associated with increased risk of childhood leukaemia; it is not certain the association is causal.
METHODS: We report a national case–control study relating childhood cancer risk to the average magnetic field from high-voltage overhead power lines at the child’s home address at birth during the year of birth, estimated using National Grid records. From the National Registry of Childhood Tumours, we obtained records of 28 968 children born in England and Wales during 1962–1995 and diagnosed in Britain under age 15. We selected controls from birth registers, matching individually by sex, period of birth, and birth registration district. No participation by cases or controls was required.
RESULTS: The estimated relative risk for each 0.2 mT increase in magnetic field was 1.14 (95% confidence interval 0.57 to 2.32) for leukaemia, 0.80 (0.43–1.51) for CNS/brain tumours, and 1.34 (0.84–2.15) for other cancers.
CONCLUSION: Although not statistically significant, the estimate for childhood leukaemia resembles results of comparable studies. Assuming causality, the estimated attributable risk is below one case per year. Magnetic-field exposure during the year of birth is unlikely to be the whole cause of the association with distance from overhead power lines previously reported from this study.