Severe limitations of ecologic data

[epirad@mchsi.com]

Dr. Cohen,



I have made every effort to explain my concerns in detail (including many 

references) regarding your use of ecologic studies to test the LNT. In my 

opinion, these discussions have little to do with the LNT, but rather the 

limitations of using ecologic data. For example, how can surrogate county 

smoking data be used to treat the confounding in your relationship for people 

who have smoked 30 years or more at various rates per year? Your surrogate 

data represents a relatively short time period and we have no idea whether or 

not it actually reflects the relevant smoking information in a county.  What 

evidence can you provide to me that your ecologic data is accurate enough to 

test the LNT?  Your previous statements that your large data set allows the 

errors to average out is scientifically ungrounded. 



I have presented evidence that your smoking data does a poor job of explaining 

the variation in lung cancer noted for your counties. Dr. Puskin has presented 

further information that suggests your findings are due to residual 

confounding by smoking.  Further, I have presented information that your 

mortality estimates do a poor job of predicting the actual incidence rates for 

a county for the time period of interest. 



Your continued comparisons to case-control studies have little to do with 

determining whether or not your data are rigorous enough to use to test the 

LNT. Do you understand that ecologic studies are subject to cross-level bias 

which can cause unbounded bias in either the negative or positive direction, 

while this is not a problem with case-control studies? You already stated you 

can not use your ecologic study to examine the dose response for radon.  As 

Dr. Mossman pointed out in this months HP Newsletter, if you can not use it to 

examine a dose response for radon you can not use it to test the LNT since 

what is the LNT but a dose response.  



Perhaps your lack of understanding of my views is a result of a general 

failure to acknowledge the limitations of your ecologic data. If you can not 

acknowledge the limitations of ecologic data, there really is no need to 

continue this dialogue.  Let's both move on to more constructive use of our 

time. 



Respectfully,  Bill Field

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

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/