Subject: How important is the "mechanism?"....
Date: Fri, 3 Jul 1998 053522 -0500 (CDT)
From: "Roy L. Beavers" <rbeavers@llion.org>
To: emfguru@hotmail.com
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---------- Forwarded message ----------
Date: Thu, 2 Jul 1998 12:42:03 -0700 (PDT)
From: marjorie lundquist
To: rbeavers@llion.org
Subject: Re: The "way" of politicians
Although Bill Curry and I are both physicists, I don't share his
strong desire to know the mechanism by which electromagnetic fields
cause harm to living tissue. I don't agree that epidemiological
studies don't mean much in the absence of a mechanism of injury.
Bill is correct that one cannot conclude, on the basis of
epidemiological data alone, that a given agent is hazardous to health.
All that epidemiological studies can document is association.
In some cases, if the association is specific enough, the causal agent
can be pretty clear. I am thinking of a map prepared of cases of
illness in Guilford, CT, which showed that the cases were all located
along a particular electric power line, within a certain distance of
it. In this particular instance, the way the diseases were
geographically associated with that power line made it pretty apparent
that the power line was implicated.
But more often there are a variety of possible agents that might be
responsible for a given observed pattern of disease, and the
epidemiological study usually will not distinguish among them.
This is when one looks to supporting evidence that may enable one
agent to be selected as more credible than another, in terms of
causing the disease. Then the question of mechanism is often raised,
and if there is no known mechanism by which one of the suspect agents
could cause the disease in question, there will be some
people--including some scientists--who will rule out a candidate agent
on that basis!
The question of mechanism does call for an answer, but it is not
absolutely essential. With microwave EMF, for example, we have one
(and I think two, although the second is somewhat controversial at
present) controlled laboratory studies that indicate an association
between lifetime rodent EMF exposure and disease (specifically, cancer).
The value of the controlled laboratory study is that it can answer the
question: Is the disease clearly associated with the particular agent
under study here? With one of the rodent studies (the Guy rat study)
the answer is YES, the cancer rate is about 3 1/2 times higher in the
rats that received the microwave exposure and if the data reported in
Microwave News (March/April 1997) is correct, then the answer in the
Toler mouse study is again YES, there is a higher cancer rate in the
microwave-exposed mice than in the control group.
An epidemiological study CANNOT pinpoint one specific agent as causing
the pattern of disease; a controlled laboratory study CAN.
Once we know, from controlled laboratory studies, that cancer really
is associated with EMF exposure, and not some other environmental
agent, then we can go back to the epidemiological studies with new
assurance that we can tie the disease to a specific agent (via
controlled lab studies). Now we can draw additional conclusions from
the epidemiological studies -- and nowhere in here do we have to know
a mechanism!
Having pointed out that knowledge of a mechanism is not logically
necessary in order to give epidemiological studies credibility, I must
now point out that Bill Curry's viewpoint is held by a good many
professionals, especially physical scientists. They simply are not
going to believe that a hazard exists unless someone can give them a
credible mechanism!
In the final analysis, credibility is personal. I may be convinced by
one set of data, but my neighbor or a colleague may require completely
different evidence in order to be convinced. When the situation is
not clear and professionals disagree, then the only way to convince a
large number of people (which is usually necessary as a prerequisite
to political action) is to have reasonably convincing evidence on
EVERY front!
So Bill Curry's emphasis on mechanism is appropriate, even though I
personally don't perceive it as necessary and don't need it to
convince ME! Attention to the mechanism by which EMF exposure
produces disease is important and proper, even though it isn't
logically necessary, and even though (in my judgment) we have enough
evidence RIGHT NOW to convince any sensible person that exposure to
microwave EMF is hazardous!
--Marjorie
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Reprinted with permission of Roy Beavers, http://www.feb.se/EMF-L/EMF-L.html