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From: dadams@cherry10.cray.com (David Adams)
Newsgroups: sci.electronics
Subject: Re: Re:High Tension Wire Hazards
Message-ID: <112256.27482@timbuk.cray.com>
Date: 18 Apr 91 17:34:54 GMT
References: <4023@anasaz.UUCP>
Reply-To: dadams@cherry10.cray.com (David Adams)
Organization: Cray Research, Inc.
Lines: 38


Yesterday I heard a report on the radio about a study on the 
Hazards of living near high tension wires.

The study involved, the report pointed out, was not scientific!
In order to perform a valid scientific study on the subject
we would have to obtain a random sample of children, randomly
assign half of them to live near high tension wires and the 
other half away from high tension wires.  Then we follow the
progress of these children over the course of many years and
measure the proportions which develope cancer, etc.

We cannot do this in a democratic society.  So what the researchers
did was to find a group of people who had developed some disease.
(I don't remember what disease was involved.)  Then they tried to
find a *similar* group of people who did not develope the disease.
Then they looked back to the childhood histories of these people
to see how many of each group lived near high tension wires.

This is not a good scientific method.  It was pointed out, for example,
that it may well be that more affluent people were willing to 
volunteer for the study, and that fewer of these were likely to have
lived near high tension wires.  When you set out to find a *similar*
group, it is entirely impossible to consider all of the variables
that might be involved.  This is one of the reasons that randomization
is so critical.

When I see so many people begin to believe conclusions that come 
from bogus studies, it really makes me stop and think.  We need to 
learn to be critical when we read, or evaluate a study like this one.
This doesn't mean that High Tension Wire Hazards do not exist, but
we cannot use the conclusions of experiments like these as evidence
that they do.  


David Adams
Statistical Analyst
Cray Research Inc.