RE: LINEAR MODEL

["Weiner, Ruth" <rfweine@sandia.gov>]

No! Linear non-threshold means linear through the origin (no threshold).
There are pollutants that have a linear dose-response with a threshold -- CO
is one!  For all I know, so is ionizing radiation! The equation for a such a
situation would be x = ay + b where x=b, x=dose, y=response, where x=b is
the threshold dose and dx/dy = a.

Ruth F. Weiner, Ph. D.
Sandia National Laboratories 
MS 0718, POB 5800
Albuquerque, NM 87185-0718
505-844-4791; fax 505-844-0244
rfweine@sandia.gov


-----Original Message-----
From: Wes Van Pelt [mailto:vanpeltw@idt.net]
Sent: Thursday, May 06, 1999 6:43 PM
To: Multiple recipients of list
Subject: Re: LINEAR MODEL


"Fritz A. Seiler" wrote:

> In a private e-mail to me, GACarlson@aol.com wrote:
>
> > Perhaps, we are just jousting over semantics, but I teach my students
> that x+ y
> > = 2 does not pass through the origin, but is still linear.
>
> I think this comment and its resolution may be of a more
> general interest, because I hear this argument altogether
> too often. So let us see:
>
> Mathematically,  x + y = 2  is the equation of a straight line.
> So you are teaching your students right, Glenn.  Take note,
> however,  that you are talking about the purely mathematical
> property of an equation.
> The linear model of radiation carcinogenesis, on the other
> hand, is NOT given by any old straight line! It  is given by a
> straight line through the origin. Thus the linear model is given
> by  y - ax = 0.  Then, and only then, will the often cited model
> property be true that twice the dose leads to twice the  risk.
> Thus a straight line is one (mathematical) thing, the linear model
> of radiation carcinogenesis is quite another (radiobiological)
> thing.
>
> Best regards
>
> Fritz

Fritz and all,
I think I see your point. But, why do we always refer to the "Linear
Non-threshold Model" rather than just the "Liner" model.  If what you say is
true, there could be no such thing as a "Linear Threshold" model.  And we
should refer to the LNT model as just the L model.
Regards,
Wes
--
Wesley R. Van Pelt, Ph.D., CIH, CHP            KF2LG
President, Van Pelt Associates
Radiation Safety and Environmental Radioactivity
mailto:vanpeltw@idt.net    http://idt.net/~vanpeltw/


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