Re: Rocketdyne Worker study

[John Goldsmith <gjohn@bgumail.bgu.ac.il>]

Otto:
    I strenously object to the last paragraph of your message.  Who has
discredited the work on prenatal exposure, and how does this derive from
what sort of selection bias?  Finally, what your learned at ICRP is 
either gossip or worthless hearsay unless you are willing to document it.
Regardless of our feelings, let us adhere to conventions relative to 
scientific evidence. Your comments on the Rocketdyne report, of which I
don't yet have a copy will be seriously considered.
         John Goldsmith, M.D., M.P.H.  gjohn@bgumail.bgu.ac.il
          

On Wed, 5 Nov 1997, Otto G. Raabe wrote:

> 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
> 		******************************************************
>