Re: Cancer Assessment Press Release

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

January 30, 1998
Davis, CA

Yes, to avoid the "healthy worker effect" the epidemiologist divides the
workers in a specific plant into groups as a function of exposure doses and
makes comparisons between these groups. This is a fine approach as long as
confounding factors that also vary be group are accounted for. 

But, the confounding factors are harder to evaluate that just exposure dose
and cause of death. Hence, important confounders such as cigarette smoking
and chemical exposures are rarely properly handled. Lung cancer is
primarily caused by cigarette smoking, so an observed increase in lung
cancer in higher dose groups is useless unless the actual smoking history
of each person in the group is evaluated. Leukemia is more readily causes
by low doses of organic solvents, such as benzene, than from low doses of
ionizing radiation. Observations of leukemia increases in higher dose
groups are not meaningful unless chemical exposures are properly evaluated
for these same persons.

Otto
		*****************************************************
		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