Thursday, August 23, 2007

A familiar dirge: "Powerline cancer risk"

There is such an obsession about this that all the disconfirmatory evidence just seems to spur fresh "data dredging" -- and if you look at enough data often enough you will find occasional examples of the correlations you seek by chance alone. Note my post of May 15th showing no adverse effects of heavy exposure among Danish electricity workers. In connection with that I am going to make a small logical point that is probably beyond the comprehension of any epidemiologist but which others should grasp:

If X is caused by Y, then ALL instances of Y should cause at least some X. If there is just ONE occasion where Y has not caused any X at all among anybody, then it shows that X is NOT caused by Y. You need only one disproof. So the Danish study junks the "carcinogenic electricity" hypothesis. Even if there are LOTS of other occasions when X and Y occur together it proves nothing.

See also the article excerpted immediately below this one

PEOPLE who live close to high-voltage powerlines during childhood are up to five times more likely to develop cancer, according to Australian research. The Tasmanian study of more than 850 patients adds weight to the link between electromagnetic fields and cancers such as leukaemia, lymphoma and multiple myeloma. It is still not known whether there is a cause and effect relationship.

Those who lived within 300 metres of a powerline up to the age of five were five times more likely to develop cancer, while those who lived that close to a powerline at any point during their first 15 years were three times more likely to develop cancer as an adult, according to the study published in the Internal Medicine Journal.

Researchers from the University of Tasmania and Bristol University in Britain compared an existing database of all patients in Tasmania diagnosed with lymphatic and bone marrow cancers between 1972 and 1980, with controls matched for sex and age. Residential histories were then gathered. People who had lived within 50 metres of a high-voltage powerline at any time were at double the risk of developing cancer than those who had never lived within 300 metres of a powerline. For every year lived within 50 metres of a powerline, the risk of cancer increased by 7 per cent, the study found. There was also evidence the risk of cancer increased with higher voltages.

The lead researcher, Professor Ray Lowenthal, from the University of Tasmania, said the debate about possible carcinogenic effects of electromagnetic fields had been going for more than 20 years. "The evidence of detrimental long-term health effects is far from conclusive and international guidelines for limiting exposure to EMF are based on possible short-term effects rather than longer-term disease risks such as cancer," Professor Lowenthal said.

People who lived near powerlines tended to be from lower socioeconomic backgrounds, although the study had attempted to control for this and the occupational risk of cancer. [A rare element of sophistication -- even if the control was only an "attempt"] "Despite the limitations of this study . our novel finding that the risks of adult leukaemia and lymphoma are most strongly associated with early childhood exposure to powerlines deserves further study at both the population and laboratory levels."

Bruce Armstrong, Professor of Public Health at Sydney University said the study was consistent with previous research. "I think we are in a position where we have to say that there is a possibility that exposure to electromagnetic fields increases the risk of some cancers, but I don't think we know yet whether powerlines actually cause cancer." [Rather a non-statement]


Media reports bias people away from evidence and towards belief in scares

As an example, nothing could be better substantiated than the uselessness of a low-fat diet but almost nobody seems to be aware of that

Recently a friend mentioned that he was concerned about health effects from wifi. I pointed out that this was likely an overblown concern, fed by the media echoes of a scare mongering BBC Panorama program, and pointed him at the coverage at Ben Goldacre's blog Bad Science for a through takedown of the whole issue. To my surprise he came back more worried than ever. He had watched the program on the Bad Science page, but not looked very much at the damning criticism surrounding it. After all, a warning is much more salient than a critique.

My friend is highly intelligent and careful about his biases, yet fell for this one. There exists a feedback loop in cases like this. The public is concerned about a possible health threat (electromagnetic emissions, aspartame, GMOs) and demand that the potential threat is evaluated. Funding appears and researchers evaluate the threat. Their findings are reported back through media to the public, who update their risk estimates.

In an ideal world the end result is that everybody get better estimates. But this process very easily introduces bias: the initial concern will determine where the money goes, so issues the public is concerned about will get more funding regardless of where the real risks are. The media reporting will also introduce bias since the media favour reporting newsworthy news, and risk tends to cause greater interest than reports of no risk (or the arrival of reviews of the state of the knowledge). Hence studies warning of a risk will be overreported compared to risks downplaying it, and this will lead to a biased impression of the total risk.

Finally, the public will have an availability bias that makes them take note of reported risks more than reported non-risks. And this leads to further concerns and demands for investigation. Note that I leave out publication bias and funding bias here. There may also be a feedback from the public to media making media report things they estimate the public would want to hear about. These factors of course muddy things further in real life but mostly seem to support the feedback, not counter it.



Just some problems with the "Obesity" war:

1). It tries to impose behavior change on everybody -- when most of those targeted are not obese and hence have no reason to change their behaviour. It is a form of punishing the innocent and the guilty alike. (It is also typical of Leftist thinking: Scorning the individual and capable of dealing with large groups only).

2). The longevity research all leads to the conclusion that it is people of MIDDLING weight who live longest -- not slim people. So the "epidemic" of obesity is in fact largely an "epidemic" of living longer.

3). It is total calorie intake that makes you fat -- not where you get your calories. Policies that attack only the source of the calories (e.g. "junk food") without addressing total calorie intake are hence pissing into the wind. People involuntarily deprived of their preferred calorie intake from one source are highly likely to seek and find their calories elsewhere.

4). So-called junk food is perfectly nutritious. A big Mac meal comprises meat, bread, salad and potatoes -- which is a mainstream Western diet. If that is bad then we are all in big trouble.

5). Food warriors demonize salt and fat. But we need a daily salt intake to counter salt-loss through perspiration and the research shows that people on salt-restricted diets die SOONER. And Eskimos eat huge amounts of fat with no apparent ill-effects. And the average home-cooked roast dinner has LOTS of fat. Will we ban roast dinners?

6). The foods restricted are often no more calorific than those permitted -- such as milk and fruit-juice drinks.

7). Tendency to weight is mostly genetic and is therefore not readily susceptible to voluntary behaviour change.

8). And when are we going to ban cheese? Cheese is a concentrated calorie bomb and has lots of that wicked animal fat in it too. Wouldn't we all be better off without it? And what about butter and margarine? They are just about pure fat. Surely they should be treated as contraband in kids' lunchboxes! [/sarcasm].

Trans fats:

For one summary of the weak science behind the "trans-fat" hysteria, see here. Trans fats have only a temporary effect on blood chemistry and the evidence of lasting harm from them is dubious. By taking extreme groups in trans fats intake, some weak association with coronary heart disease has at times been shown in some sub-populations but extreme group studies are inherently at risk of confounding with other factors and are intrinsically of little interest to the average person.


1 comment:

Bari2K said...

"If X is caused by Y, then ALL instances of Y should cause at least some X. If there is just ONE occasion where Y has not caused any X at all among anybody, then it shows that X is NOT caused by Y. You need only one disproof."

Simply wrong. Good logic, bad science.

The logic is perfect but real world has more than two factors like X and Y.

This is a better statement:

"If X is caused by Y in absense of {Z}, then ALL instances of Y should cause at least some X if {Z} is not present. If, in absence of {Z}, there is just ONE occasion where Y has not caused any X at all among anybody, then it shows that X is NOT caused by Y. BUT if there is at least one of the Z factors present then you need more experimentation"

{Z} is the set of factors which act upon X, i.e. genetic of humman group, previous exposure to another factors, history of the group under study and so forth.