[ RadSafe ] Cohen's radon results differently
chofmeyr at gmail.com
Sun Sep 18 14:31:28 CDT 2011
On 19th June Howard Long challenged my reminder that in Cohen's US-wide study
of domestic radon and lung cancer, there was, on average, a negative
correlation between Cohen's smoking prevalence and the average county radon
concentration. Howard wanted numbers.
On 20th June prof Cohen invited further discussion of his work. Then away on
an extended stay, I told dr Long that I will have a look when I get back home.
B Cohen and Wes van Pelt had kindly made their data available in spreadsheet
form almost a decade (and a few computers)ago. At the time and later I did
numerous plots and wrote some notes, which I now found on an archive disk.
I put some of it together in a .pdf file of about 1.5MB (attached); please
excuse some repetition in the text. If the attachment does not survive Radsafe,
then please request directly from me at webmail address below.
Some background for the younger crowd:
Cohen set out to study lung cancer rates as a function of county average
domestic radon concentration (ARC)in 1601 US counties. His null hypothesis was
presumably to justify LNT (Linear No-Threshold model of carcinogenesis).
However, fate stacked the cards in that smoking prevalence, as determined by
him, was to a degree anti-correlated with average county radon. Due to the
carcinogenic strength of smoking, the raw data naturally reflected an
anti-correlation with radon concentration.
This meant that the lung cancer data would have to be carefully corrected to
extract a 'real' correlation, which Cohen probably only realized when he was
analyzing the data. Cohen tried more than one avenue to assess smoking
and he was obviously reasonably satisfied with his final choice, although his
correction strangely left the anti-correlation practically unchanged.
Having investigated lung cancer (LC) - Cohen's and Van Pelt's data - also in
relation to elevation and county population size, I am practically forced to
the conclusion that there appears to be a strong smoking residual even after
the correction. LC shows an even stronger anti-correlation with altitude below
1260ft than with radon (ARC) below about 3pCi/L,yet (LC) proves
independence of both.
Cohen tested several hundred possible confounders, but very few
managed to turn the LC
correlation with Average radon positive.
I would respectfully ask prof Cohen: SUPPOSE the smoking correction was
insufficient and left an implicit smoking component in the LC data?
In the notes I explain how one can use a plotting trick on Cohen's data to
evaluate LC dependence (or rather independence) on ARC even without a smoking
correction to the LC data - and consequently dispose of LNT.
chris.hofmeyr at webmail.co.za
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