Re: Ecological Fallacy?

["Otto G. Raabe" <ograabe@ucdavis.edu>]

February 25, 1998
Davis, CA

If you know only the average concentration of radon in a large group of
homes and you also know only the average incidence of lung cancer among
people living somewhere in those homes, you cannot say what concentration
of radon is associated with those cases of lung cancer. That would be the
"ecological fallacy". Some of the homes may have high levels of radon, and
some may have low levels. 

In a case control study you could look at a selection of individuals in
those homes that developed lung cancer and measure the specific radon
concentration in each of their specific homes. You could match these cases
with people who have similar lifestyle and background and have lived to the
same age, and you could see whether these people (the controls) had higher
or lower radon levels in their homes. If the radon levels in the homes of
the lung cancer cases tend to be significantly higher or lower than in the
homes of the controls, you could report a mathematical association of radon
concentration with the development of lung cancer. Causation would be
plausable, but not proved by such data, however.
		*****************************************************
		Prof. Otto G. Raabe, Ph.D., CHP
                [President, Health Physics Society, 1997-1998]
		Institute of Toxicology & Environmental Health (ITEH)
		     (Street address: Old Davis Road)
		University of California, Davis, CA 95616
		Phone: 530-752-7754  FAX: 530-758-6140 [NEW AREA CODE]
		E-mail ograabe@ucdavis.edu