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Power Lines, Cancer and the Meaning of Statistics

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Another day, another bunch of medical results draped in statistics. What is the right way to interpret them?

This article on Power Lines and Cancer provides the basic tools. In a sentence: take with a grain of salt all results based purely on statistics, where the risks or the benefits are less than 300%.


Do overhead Power lines cause cancers, especially leukaemia in children?

Like in a “Rosenkrantz and Guildenstern” match of oratorical tennis, two sides of a supposedly scientific debate have not been able to get down to a reasonable conclusion after 30 years of research.

One month, we are told that Science has demonstrated that Power Lines induce leukaemia and other diseases. Cue schools asking for pylons to be removed; and people selling their houses before values start sliding down.

The following month (or year), we are told that scientific studies have shown that the danger, if it exists, is not discernible at all. Cue schools asking for pylons to be removed anyway. And so on and so forth.

How can one make any sense out of this? After all those children either get, or do not get leukaemia. Should that be a matter of debate?

In an era where Science appears to be tugged in all kinds of directions (think of the MMR vaccine debate; the forecasted disasters of Climate Change; the purported obesity epidemic), an analysis of the Power Lines and Cancer debate can teach important lessons on the limits of translating Science into Policy; the need to exercise critical thinking, also about “Authorities”; the perils of letting the media interpret the world for you; and the danger that scientific analysis, endlessly manipulated by unscrupulous hacks and pressure groups, will be used to dent our freedom.

The Science

Studies on adverse effects of electromagnetic fields have been concentrating recently on Power Lines and Mobile Phones [2]. Power Lines are a source of electrical and magnetic fields in their proximity and these can interact with biological material [8]. However, for the frequencies and strengths involved with overhead Power Lines, there is no indication from laboratory studies of any negative effect, for example on rats or cell cultures.

An alternative line of investigation is through epidemiological studies, using statistics to identify adverse effects if any. For example, an increase on the incidence of diseases in children living near Power Lines (“cases”), compared to children living far away from them (“controls”).

Results are usually provided in terms of Relative Risk (RR), the ratio between the percentages of people developing an illness among the “cases” and among the “controls”. A value of 1.0 for RR means there is no difference between cases and controls. A value less than 1.0 indicates that the “cases” are safeguarded against the illness more than the general population. A value above 1.0 is evidence that the “cases” are at greater danger to fall ill than usual.

For example, the RR of developing lung cancer is around 40 23 for habitual (male) smokers. In other words, a smoker’s chance to get lung cancer is 2,300% that for a non-smoker.

The first report on higher leukaemia rate for children living near high-voltage Power Lines is the Wertheimer & Leeper study of 1979 and another by Savitz et al. in 1988 [2]. Much work has been done afterwards by organizations such the US-based Institute of Electrical and Electronic Engineers (IEEE) mostly disproving the findings above. The United Kingdom Childhood Cancer Study UKCCS (UKCSS) found no evidence for increased “risk for childhood leukaemia, cancers of the nervous system, or any other childhood cancer” in reports in 1999 (about electricity supply), in 2000 (proximity to electrical installations including Power Lines) and 2002 (electric fields in general) [5].

The most important recent scientific epidemiological results for Power Lines and cancer have been published in June 2005 by Professor Gerald Draper of the University of Oxford’s Childhood Cancer Research Group [4]. In the study:

• Children within 200 m of high-voltage Power Lines had a relative risk of leukaemia of 1.69
• Those between 200 and 600 m had a RR of 1.23. This is not compatible with current knowledge on biological effects of magnetic fields. At 200 m, fields from Power Lines are less than the average fields in homes from other sources.
• RR appeared to decrease with distance. There is less than 1% probability that this finding is purely due to chance (an estimate usually indicated with “p<.01”)
• No excess risk for other childhood cancers correlated to proximity to lines

Conflicting interpretations

At first glance, there may be something about children leukaemia, likely associated to proximity to Power Lines. Still, there is no known mechanism, and the relative risk is minimal. As pointed out in the editorial accompanying the Draper article, Power Lines may account (if they do) for no more than five cases of disease per year in the UK, compared to more than 200 children dying because of traffic accidents, and 32 in house fires [8]. Furthermore, there is no indication of effects for any other form of cancer [5]. This means that at present there is no incontrovertible data clearly indicating a cancerous danger in power lines for children and adults.

But it is not possible to design a study proving the negative, that Power Lines do not cause any risk of cancer. The consequence is that the public controversy is likely to stay with us for the foreseeable future. The diversity of comments to the Draper study is in fact truly remarkable [4].

Take for example the opinion of Denis Henshaw, Professor of Human Radiation Effects at the University of Bristol [3] (my emphasis): “[Draper’s] latest findings not only strengthen further the evidence that children living in proximity to high voltage power lines are at increased risk of childhood leukaemia, but in finding effects up to 600 metres away they invoke electric field corona ion effects as a possible causal mechanism”.

Professor Henshaw, whose work is funded by the charity “Children with Leukaemia”, goes as far as stating that “this may be the tip of the iceberg […] in terms of the many other illnesses also associated with magnetic fields such as adult leukaemia, adult brain cancer, miscarriage and depression”.

Which side is “right”? The “Authority” of the “Authorities” is not an answer: because Science is not about following the Authorities; and there are well-known scientists and organizations either side of the debate. Among those skeptical of any cancerous danger in Power Lines, the International Commission on Non-Ionizing Radiation Protection (2001); the International Agency for Research on Cancer (2001); the U.S. National Institutes of Health (2002); and the U.K. National Radiological Protection Board (2004) [8].

Obstacles on the road to a good Policy

Where Science cannot reach, opinions start kicking in, and competing interests maneuver to cajole us in one direction or the other. In the case of Power Lines and Cancer, the controversy has indeed been “sustained by uneven reporting on this issue by the mass media” and “lay-oriented books that allege that there has been a conspiracy to conceal the health risks of power-frequency fields” [8].

“Uneven reporting” is visible on the BBC News Website. Again in response to the publication of the Draper article [1], there is an article that presents the issue in scarier traits at first: “leukaemia rates are significantly higher among children who live close to power lines”.

It then progressively mellows “In the past, evidence suggested that low frequency magnetic fields, generated by high voltage cables, may be implicated in some way – a theory which hasn’t been endorsed by [Draper’s] Childhood Cancer Research Group” before ending with “we also spoke to Dr David Grant, director of the Leukaemia Research Fund. He told us he thought the higher incidence of leukaemia near pylons was a coincidence”.

Statistical indicators are explained poorly and in an alarmistic manner. For example, a Relative Risk of 1.69 is described as a 69% increased probability to develop leukaemia. Such a reporting is mathematically right, conceptually wrong and frankly misleading. Is there as 400% growth in increasing one’s savings from £1 to £4? Yes, but it’s still just £4. Moreover, as explained below, values of RR less than 3 seldom are considered worth of note in epidemiological studies.

Perhaps, given that the page is from the Breakfast section, the BBC’s was a clumsy, rather misinforming attempt at eliciting controversy and comments from the audience (see form at bottom of page). That’s bad news for present-day Britain, where its media-conscious Government gives “insufficient weight to available evidence” placing “too great a reliance on unsubstantiated reports that often have their origin in the media” [12]

There is concern also reading on the bias of the published scientific literature. For example, a study done in Montecito [6] reported as much as seven cases of children with leukaemia or lymphoma around a school in the vicinity of overhead Power Lines. However, “five of the seven Montecito children […] attended the school. Of those five, two attended the school for a very brief duration, leaving only three with plausible cases for school exposures as a possible cause” [7].

The Montecito study is one of the scientifically flawed pillars behind the most famous “conspiracy” book, “The Great Power-Line Cover-Up” written by Paul Brodeur [10]. Mr Brodeur set out to demonstrate the cancerous effects of high-voltage power lines, and to denounce a world-wide conspiracy to keep such evidence hidden from the public.

Long rebuttals have been published since [7]. In a telling sign that there may have been a case of “investigative journalism with a purpose”, few if any opinions of the “conspirators” were either solicited or included in the book, leading to a commentator to state that “Brodeur’s criticisms of the people […] are no more than unsupported innuendo, gross exaggeration, and serious misstatement.” [7].

Dealing with epidemiological studies

Epidemiology is a powerful tool. It can even provide estimation on the likelihood that the outcome of a study is due to random coincidences, rather than an actual casual link. The Draper article cited above scientifically asserts that there is less than a 1% chance (“p<.01”) that such its findings are due to a random quirk in the measurements, instead than actual physical processes.

That 1% may appear a very low figure. On the other hand, it also means that among the epidemiological studies published every year with a similar p, one out of every 100 will on average report irrelevant findings.

Trouble is, we do not know which one. An epidemiological study like Draper’s may indicate a link childhood leukaemia-Power Lines. But there is always the possibility that by a run of bad luck, that study is the one out of 100 that “got it wrong”.

And with values of p around .05, incorrect findings will affect one out of every 20 of the great majority of Power Lines and Cancer studies. This problem is further compounded by the normal “reporting bias” (when “multiple studies are done but only some are reported” [8]). A result labeled with p<.05 may have no real meaning: when 20 or more measurements are performed, one of them will be randomly positive.

With other issues at play like “confounders”, (non-electromagnetic causes like traffic density and socioeconomic class); and “publication bias” (as “positive studies are more likely to be published than negative studies”) [8], epidemiology alone cannot suffice in understanding a phenomenon. What else is needed to complement it? Here’s a checklist [7]:

1. Epidemiology should find a strong association (i.e. a high value for RR, e.g. above 3)
2. A very specific disease should be involved (for example, one type of leukaemia)
3. There should be a consistency between studies and with data from laboratory work, cancer incidence trends and other sources. In fact, “when two studies with similar designs find different results and the differences cannot easily be explained or rationalized, neither study is accepted as definitive” [7].
4. The results should be preferably not involve a rewriting of biology and physics

Obviously, an enormous RR could be used to justify investigations on how to rewrite biology and physics. Vice-versa, a very plausible biological mechanism only needs a relatively low value for RR.

Future investigations?

As of June 2006 criteria 3 and 4 (consistency and plausibility) are still missing, and relative risks are no more than 1.5-2.5 (sometimes, they are less than 1.0).

More of the same types of epidemiological studies are unlikely to resolve anything [8]. Decades of laboratory studies have shown “little evidence of a link between power-frequency fields and cancer” even in “life-time exposure of animals”. And despite the increasing use of electricity, a 1993 report by the World Health Organization and an analysis for Sweden from 1960 to 1991 have found no discernible changes in leukaemia incidence in adults or children [7].

Perhaps it may be interesting to finally identify the role of the “confounders” [8]. But this may be like shooting in the dark: and there may really be no need to invest resources in trying to identify a link between Power Lines and Cancer.

Lessons learned

One side of the debate states that leukaemia cases do not depend on the presence of overhead power lines: because there is no evidence in that direction. The other side goes as far as to say that children, if not everybody, should be kept at distance from those same lines, in order to lessen the chances of getting leukaemia and other disease: because there is no evidence that power lines are safe.

I do not see any reason to fear power lines. More in detail: for power-line-induced leukaemia to be actually happening, a small, yet peculiar but not impossible rewrite of biology and physics is necessary. We would need very hard evidence to back that up. And there are a lot of other causes of deaths that kill much more than 5 children per year in a country like the UK.

An opinion, but that is the whole point. The problem is if and how we translate a potential risk into a policy, a set of guidelines defining our course of action. If we leave the interpretation to interested parties and sensationalistic media, they will be in charge of regulating our lives in ways unwarranted by our own scientific data.

Do we have to evacuate all areas around power lines because there is some possibility that they will cause leukaemia? Or should we agree that it is much wiser to keep living our lives, unless something is ultimately proven dangerous? To put it simply: shall we move forward only if we can get an “all clear”? Alternatively, shall we stay put only if there is any clear danger in moving?

Are we for being very cautious, or ready to embrace progress? The natural answer for Humanity seems to be the latter. Our brains are hard-wired into recognizing and appreciating the novelties in our environment. From very early childhood, we find it natural to explore, investigate. And walk. Who among us would refuse to walk until checking the ground ahead at every step?

Some have suggested to resolve the controversy by implementing “Prudent Avoidance”, one kind of Precautionary Principle, “taking steps [of modest costs] to keep people out of fields, both by re-routing facilities and by redesigning electrical systems and appliances” [7]. For example, underground lines have been suggested. But they are expensive, and “difficult, time-consuming and expensive to repair […] (and they do break)” [8].

“Prudent Avoidance” is quite dangerous for a free society [12]. It may end up becoming the hijacking tools for vocal individuals and organizations to lock up resources that could be better spent in making everybody’s lives freer and easier, instead of in the futile attempt to eliminate all chance of risk.


The Power Lines debate is not just about electrical power, and is not just about personal choice. It is a matter of societal power.

The definition of the very rules governing our society is at stake: if the Ultra-cautious Party wins, it will be one of the first steps in the future prohibition of most of what it is new. After all, who can demonstrate that there is no danger at all in using WiFi to get to the Internet? Or that there are no negative consequences in distributing ideas through online magazines?


[1] Power lines and childhood cancer, Friday, 3 June, 2005, from the BBC Breakfast programme

[2] Michel Ianoz, ‘Biological And Health Effects Of Electromagnetic Fields’, IEEE EMC Society, 2004

[3] Reported in “Responses to the CCRG study of power lines and childhood cancer”

[4] Gerard Draper et al., ‘Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case-control study’, British Medical Journal 2005; 330: 1290

[5] ‘EMFs and childhood cancer’, by the British company National Grid’s EMF Unit Public Information Line

[6] R Kreutzer et al., ‘Investigation of the Montecito Leukaemia and Lymphoma Cluster Final Report [Draft]’, California Department of Health Services, 1990

[7] R D Miller, ‘Unfounded Fears: The Great Power-Line Cover-Up Exposed’, IEEE EMBS Committee on Man and Radiation (IEEE, 1998)

[8] J Moulder, ‘Power Lines and Cancer FAQs’, Medical College of Wisconsin, Milwaukee, Wisc, U.S.A,

[10] P Brodeur, ‘The Great Power-Line Cover-Up’ (Little, Brown 1993)

[12] J Luik, “Risk vs. Liberty”, TCS Daily, 27 June 2006

Written by omnologos

2007/Sep/12 at 22:22:23