Re: ecological fallacy and the LNT

[BERNARD L COHEN <blc+@PITT.EDU>]

	If one assumes LNT, the "ecological fallacy" does not apply, and

either of your deductions is sound. If you do not assume LNT, there is no

useful meaning to collective dose, such as man-rem.

	The "ecological fallacy" comes into play if you are trying to find

a dose-response relationship for individuals, without prior prejudice

about the shape of the curve. As a simple example, if the dose-response

relationship is risk = 0 for dose less than D, and risk = R for dose

greater than D, the cancer rate in a county would depend on the fraction

of the population exposed to doses greater than D; if one uses

ecological data, one would assume that the cancer rate depends on the

average dose, which could be very different and therefore wrong. Doing the

latter is the ecological fallacy. Obviously, in this example, LNT is wrong

since there is a threshold. In my work, I assume LNT to test its validity.

	In recent years, many epidemiologists have stretched the

definition of the "ecological fallacy" to include treatment of confounding

factors. They point out that it is not correct to assume that confounding

effects depend on average values of variables. For example, if personal

income is an important confounding factor, one cannot assume that its

confounding effects are taken into account by use of average income for

the county; the confounding may depend on what fraction of the population

is very rich, or very poor. My methods of treating such problems are

explained in my paper on "Treatment of confounding factors in an

ecological study" which I sent you and which is posted on my web site.

Several other aspects of this extended definition of the ecological

fallacy are also treated there, and in my other papers.



Bernard L. Cohen

Physics Dept.

University of Pittsburgh

Pittsburgh, PA 15260

Tel: (412)624-9245

Fax: (412)624-9163

e-mail: blc@pitt.edu





On Tue, 12 Feb 2002 RuthWeiner@AOL.COM wrote:



> Dear RADSAFERs

>

> I am working my way through both Field et al (and some ancillary papers

> kindly sent me by Dr. Field) and Dr. Cohen's papers (thatnk you, Bernie, for

> sending them).  I am trying to understand the papers with all their nuances.

> I believe this can be done by a reasonably competent scientist like me (Ph.

> D. -- chemistry) without special training in epidemiology, but from time to

> time I will post questions -- real questions to which I would like real

> straightforward answers -- on RADSAFE.  Let me say at the outset that these

> questions are not intended to castigate anybody or take sides.  If I use the

> LNT in a question, it doesn't mean I endorse it.   The questions are for

> information.   (and if they sound repetitive to the individual who accused me

> of "me too-ism" well, that can't be helped).  So here is my first question,

> about the "ecological fallacy."

>

> Let us say the cumulative dose to a population of 10,000 persons is 1000

> PERSON-rem.  Then, according to the LNT, one might expect 0.5 excess cancer

> in that population of 10,000 (0.0005*1000 = 0.5).  One can also,

> independently, say that the average dose is 0.1 rem (1000/10,000 = 0.1), or

> 100 mrem.  But to say that therefore the average expected cancer incidence

> would be 0.000005 (0.0005*0.1) is the fallacy in question.  Essentially,

> "average individual cancer expectation" or whatever is meaningless.  Have I

> got it right?  If not,what is my mistake?

>

> (The LNT conversion from rem to cancer is from ICRP 90, page 22)

>

> Ruth Weiner, Ph. D.

> ruthweiner@aol.com

>



************************************************************************

You are currently subscribed to the Radsafe mailing list. To unsubscribe,

send an e-mail to Majordomo@list.vanderbilt.edu  Put the text "unsubscribe

radsafe" (no quote marks) in the body of the e-mail, with no subject line. You can view the Radsafe archives at http://www.vanderbilt.edu/radsafe/