Intended for healthcare professionals


Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case-control study

BMJ 2005; 330 doi: (Published 02 June 2005) Cite this as: BMJ 2005;330:1290

reply to authors' reply

In their reply to responses received, the authors say:
"O’Carroll’s calculations are based on the assumption that the results at
0-200 metres are due to magnetic fields while those at 200-600 metres are
due to chance. We do not think it justifiable to make an arbitrary
division of our results into two bands."

I made no such assumption. I simply estimated how much of the
associated excess incidence found by the authors would be in the range 0-
200 metres. On that point I concluded "So the stronger statistical
findings in the range 0 - 200 metres alone support about half the
increased attribution".

I made no such arbitrary division. The authors made the division in
presenting their results. I made comments on the statistical nature of
their results so divided. I made only tentative conclusions about possible
reasons for their results and I made no assumptions about causation. Far
from using arbitrary banding or incurring statistical effects of so doing,
I cautioned against taking the results from 200 to 600 metres out of
context to support or deny an effect.

Finally, I was careful to distinguish between association and cause,
contrary to the general allegation which the authors make against several

Competing interests:
None declared

Competing interests: No competing interests

20 July 2005
Michael J O'Carroll
Professor Emeritus
Garden House DL6 2SE