Re: LNT and Public Fear

[Bob Hearn <rah@america.net>]

Dear John-

If I understand the thrust of your comments, the position is 1)that the
tools of epidemiology cannot be applied to prove a negative finding or
absence of phenomenon; and/or 2)epidemology cannot confirm that
_absolutely_no_ occurence will be manifested below a threshold. I believe
that the only claim to be made is that of certainty at a given level of
confidence, a limitation which also applies to experimental findings. I
would think that an epidemiological result can be obtained for lack of
occurence below a threshold as well as it can for positive observations at a
higher level, subject to the same complications of population variability.
Please clarify or indicate if you are refering to practical limitations of
statistics at baseline levels.

Regards,

Bob Hearn

At 02:28 AM 10/14/96 -0500, you wrote:
>Dear Mark:
>     While I agree with your conclusion and much of your logic, I must,
>as an epidemiologist, deny that epidemiological observations are the 
>sources of thresholds for hazardous chemicals or carcinogens.  It is 
>experimental work that allows, under the circumstances of the experiment,
>the statement that a threshold has been established.  

>                                                 Population variability
>in responsiveness is the major logical reason for epidemiology being 
>unable to establish a threshold.  Epidemiologic observations often can 
>affirm that in a comparable population to the one studied, effects will occur 
>at a given level of exposure, but it can     never     show that no
unfavorable 
>effects will occur below a given exposure level.

> (Which is what I 
>understand a threshold to mean).  Finally, epidemiology can, under some 
>circumstances, estimate the dose or exposure which would be associated 
>with a lifetime increased incidence of a small number of cases, say 2-4 
>per million.  In my view, at least, thresholds can only be based on 
>epxperimental exposures, and are valid for sufficiently similar exposures;
>it follows that experimental exposure of human populations to radiation 
>are fraught with ethical problems, hence, thresholds for such exposure 
>are not feasible.
>    gjohn@bgumail.bgu.ac.il   John Goldsmith, M.D., Professor of Epidemilogy,
>                              Ben Gurion University of the Negev
>On Sun, 13 Oct 1996 MarkH@MAIL.KIDS.USYD.EDU.AU wrote:
>
>> Friends, 
>> 
>> I feel that Dave Scherer's thoughts are on the right track.   
>> 
>> As in the case of hazardous chemicals and/or carcinogens, a "threshold"
>> will be determined from epidemiological observations (i.e. of populations).
>> The risk threshold therefore applies to the population, and cannot directly
>> be applied to the individual. How many members of the public will
>> appreciate this subtlety ? 
>> 
>> I suspect that, were a threshold introduced, many members of the public
>> would still reason along the lines : "if 20 units is not safe, then can
10 units
>> be completely safe ?".  (I guess this might not be the case if there were
>> orders of magnitude of difference between the threshold and the typical
>> exposure.) 
>> 
>> The real solution lies in educating the public.
>> 
>> 
>> Mark Hanlon,
>> Radiation Safety Officer,
>> The New Children's Hospital,
>> P.O. Box 3515,
>> PARRAMATTA, NSW, 2124
>> Australia
>> 
>> 
>> 
>
>