Mr. Ford and Iowa Radon Lung Cancer Study

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

At 11:31 PM 01/24/2002 -0600, Michael Ford wrote:


> Dr. Field,
>
> Just curious.  How do you decide to place 15% of the subjects into
>
> the highest exposure category (>16.95 WLM) prior to analyzing the
>
> data??  Don't
>
> you have to determine what the highest exposure category is by analyzing
>
> the data?  Why 16.95?  Why not 16.0?  Why not 17.0
>
> WLM?  16.0 WLM would give you
>
> 4 WLM intervals.  It would seem that the uncertainty alone
>
> associated with recall would limit you to 1 significant figure.  But
>
> try as I might, I have
>
> not been able to reproduce your claim that the intervals are equivalent,
>
> not to mention the fact that there is no limit to your upper exposure
>
> category.
>
> Care to give it a try?  Maybe my abacus is missing a bead or two.


> Finally,  you cannot possibly
>
> make the claim that you controlled for smoking by using a "standard
>
> statistical method" (modeling).  Your most critical
>
> confounder is smoking!  It is an OVERWHELMING influence in your
>
> study.  It is the PRIMARY cause of lung cancer!  Your study
>
> attempts to define an
>
> association between radon and lung cancer that is, as yet, undefined, but
>
> is hypothesized to produce the same effect!  It is mind-boggling
>
> that this lung
>
> cancer study went to such great lengths to match for age, residency and
>
> number of children (was that intentional or luck?), but made little if
>
> any
>
> attempt to match for the number one cause of lung cancer.


Michael,


I keep answering these questions, but you do not appear to understand the

answers.


Let's try your first question once again.  How did we decide to

place 15% of subjects (cases and controls made up this 15%, but not in

equal number) in the upper exposure categories.  Well after the data

went through QA checks, we archived the data.  I then sat down with

the statistician and we discussed exposure categories.  I told him I

did not want to make artificial exposure categories (for example > 4

pCi/L) as some studies had done.  I asked him what percentage of

subjects (either cases or controls) would need to be in the upper

exposure category for adequate statistical power.  He thought, at

least 15% of the subjects should be there.  Therefore, we took the

top 15% of subjects based on their cumulative radon exposure and placed

them in the upper exposure category.  The remaining categories were

split as evenly as possible by cumulative exposure.  The 16.95 WLM

simply represented the lowest exposure for the top 15%.  This was

done a priori and it was the first time we actually saw the risk

estimates by category.  The National Pooling paper will have the

results for the Iowa Study based on different exposure categories that

form a common format for all the N. American Studies.


I really do not know how many times I have to say this to be

understandable to you.  When you do a population based study, it is

impossible to completely match for smoking up front.  Do you match

on years smoked, smoking rate, year started smoking, year ended smoking,

etc. - if you match on one of these, the other factors are not

matched.  A large proportion of studies adjust for smoking, not just

studies on radon.  Smoking impacts many types of cancer and all the

studies must adjust for smoking.  This is a routine process. 

The more you match, the more you get away from a population-based study.

It is not smoke and mirrors, but it would likely take you several

semesters of statistics and epidemiology to understand how it is

done.  In the Iowa study, we also performed checks for residual

confounding from smoking and no residual confounding was noted.


I have responded to your concerns (from my perspective they were in fact

gross misrepresentations) about the Iowa Study now in both a letter in

the Billet, emails directly to both you and Mr. Klein, and on

Radsafe.  If you want to carry on this discussion further, I

respectfully ask that the discussion move off this forum and respectfully

ask that you either write a letter to the American Journal of

Epidemiology or draft a letter for the Billet that has the support of the

Texas Radiation Advisory Board.  Surely, if you have time for these

discussions on Radsafe, I would think you also have time to draft such a

letter.


Regards, Bill Field

***************************************************************************************
R. William Field, M.S, Ph.D.
College of Public Health
Research Scientist - Department of Epidemiology
Adjunct Professor - Department of Occupational and Environmental Health
Graduate Faculty - College of Public Health
N222 Oakdale Hall
University of Iowa
Iowa City, Iowa  52242

319-335-4413 (phone)
319-335-4748 (fax)
mailto:bill-field@uiowa.edu
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