LNT and Collective Dose

["Field, R. William" <bill-field@UIOWA.EDU>]

Dr. Cohen,


Do you agree with the definition below for ecologic fallacy and my points

below (especially number 6) below in response to Ruth's

question?



> Ecologic fallacy is merely an
>
> inappropriate conclusion regarding relationships at the individual level
>
> based on ecological data (Kelsey et al. 1986).
>
>
> However, ecologic studies inherently have many weaknesses that lead to an
>
> inappropriate conclusion.    For example, 
>
>
> 1) in case-control studies nondifferential (or random error) exposure
>
> misclassification usually causes bias toward the null.  However, in
>
> an ecologic study nondifferential misclassification can drive either
>
> sizable under or over estimation of the exposure disease relationship.
>
>
>
> 2) Using summary measures (like sales tax to represent smoking
>
> prevalence) for a county is very inadequate to control for confounders.
>
>
>
> 3) Some factors that are not confounders at the individual level can be
>
> at the ecologic level.  To have any hope of control for confounding
>
> at the county level, you need very detailed information on the
>
> confounding and exposure variable distributions within a county. 
>
> That is why I previously suggested to Dr. Cohen that he try to obtain
>
> this information (method suggested by Guthrie). 
>
>
> 4) Jim Muckerheide often cites the large numbers of counties in Dr.
>
> Cohen's studies.  But, the availability of large numbers does not
>
> eliminate biases no matter if you had an infinite number of
>
> counties.  Large numbers do help improve the precision (narrow
>
> confidence bands), but the large numbers have no effect on reducing
>
> biases.  In other words, the finding can be precisely wrong.
>
>
>
> 5) I have seen no data from Dr. Cohen to show that the risk factors
>
> within counties are not correlated.  Unless the risk factors are
>
> purely additive (and I see no evidence of that), the dose response
>
> findings for the ecologic study will be biased.
>
>
> 6) Ruth, in your example below, the population is not at all defined so
>
> the concept of collective dose and collective risk can not be used. 
>
> Collective dose and collective risk can only begin to be considered valid
>
> if the exposed population can be well described and
>
> quantified.   For example, many groups of workers who may have
>
> a higher risk of exposure can be quantified by age, job description, sex,
>
> length of employment and a multitude of other factors.  The general
>
> (working) group I described above has many more demographic details than
>
> is available in ecologic studies.  If you don't have better
>
> demographics than are available in a county ecologic study, you likely
>
> should not be using the collective dose concept.    
>
>
>
>
>
> Best Regards, Bill
>
>
>
> ----------------------------------------
>
> At 09:45 AM 2/12/2002 -0500, 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/