Re: Rocketdyne Worker study

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

November 5, 1997
Davis, CA

Dear RadSafers:

The Rocketdyne Worker Study is subject to flawed or perhaps biased
interpretation. "The study population consisted of 4,563 employees
monitored for external radiation and 2,297 employees monitored for internal
radiation, with the second group being mostly a subset of the first." The
report of the study shows clearly that: "Compared with the general U.S.
population, Rocketdyne/AI workers monitored for external or
internal-radiation exposure experienced lower mortality rates from all
causes, and heart disease. Comparison of monitored Rocketdyne/AI workers
with NIOSH-cohort members of comparable pay type showed lower mortality
rates for all causes and heart disease, but similar mortality rates for
total cancers. Compared with either reference population, monitored
Rocketdyne/AI workers also experienced a higher mortality rate from
leukemias." However, those higher leukemia rates were not statistically
significant.

To get any significant results at all suggesting a deleterious effect from
radiation exposure, the investigators had to ignore the low cancer rates in
these workers, and limit comparisons to within the study groups. The
employees of Rocketdyne are said to show the "healthy worker effect"
justifying the ignoring of the comparisons to outside control population data.

The next step was to do many statistical tests (many more than 100 are
listed in the report) with various arbitrary lag times and look for any
significant results. By this process some were found. By grouping all
hemato- and lymphopoetic cancers into one group (including lymphosarcoma
and excluding chronic lymphatic leukemias), one group at >200 mSv external
exposure had 2 cases that were mathematically significant. These two cases
drove the trend test to be significant when lower doses were considered
that did not in themselves show any significant effect. Also, 2 persons
dies of lung cancer in the >200 mSv group. The authors seemed to be unsure
about whether prior radiation exposure could be important, so that in many
of these comparisons even significantly higher prior radiation exposures
received at some earlier job were ignored. 

To get a any significant results from the internal exposure phase of the
study, the authors has to create a special grouping of cancers called
"Upper Aerodigestive Tract Cancers". Although this is not a known target of
any of the internal emitters to which workers were exposed, they concluded
that among the 5 cases for exposures above 5 mSv that there was a
significant increase in these types of cancer compared to the 3 cases
observed in the unexposed group. It is not clear to me that the logistic
model used for these analyses is appropriate for such small numbers of
observed cases. Also, the internal dosimetry metric is not an actual
internal dose, but rather an unusual interpretation of bioassay data.

The authors did not report having looked at these few cases that drove
their findingd to see if there were other explanations for these slightly
high occurrence rates in these two particular groups. What about personal
habits? What about chemical exposures? What about adjusting the
significance levels for the fishing expedition style of epistemology?

The report of the mostly anti-nuclear advisory committee seems to a
reworking of one of Alice Stewarts old anti-nuclear essays. Unfortunately,
that highly biased advisory committee report is being widely quoted. 

I learned at the NCRP meeting last April, that Alice Stewarts pioneering
work on exposure of pregnant women to x rays with respect to childhood
leukemia has been discredited because of selection bias. Most studies by
Alice Stewart have looked for any effects that may appear to be elevated
after radiation exposure while ignoring those that may be reduced. 
		*****************************************************
		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
		E-Mail: ograabe@ucdavis.edu
		******************************************************