I was honored to be asked to contribute a chapter to the collected works within Tortured Science: Health Studies, Ethics and Nuclear Weapons in the United States, compiled and edited by Dianne Quigley, Amy Lowman, and Steve Wing, published 2012 by Baywood Publishing Company, Inc, Amityville, New York. I am very grateful that Baywood has allowed me to reprint the chapter in its entirety. The chapter is reprinted as a series of excerpts.
Loss of High Percentage of the HTDS Study Group
Of particular concern to experts and public alike was the failure of HTDS scientists to account for uncertainty due to deaths and nonparticipation. An original 5,199 people were identified as possible HTDS participants based on time and location of birth. Of these, approximately two-thirds (3,447) com- pleted the HTDS clinical exam and some withdrew after the exam. The other one-third of the originally identified potential subject group had either died before the study began or didn’t wish to participate. This is considered a rather high rate of cohort loss [59, p. 17], and this level of cohort loss can seriously bias study results, even if the losses were of equal proportions with regard to exposure or disease categories .
Experts reviewing the HTDS felt that the loss of one-third of the cohort was probably not random in ways that were relevant to the study [59, p. 17]. Those who knew or suspected that they had been exposed to Hanford radiation or who had thyroid disease may have been more likely to participate in the HTDS. Deaths may have been exposure related. (Sometimes this is called selective survival.) The review concluded “that this uncertainty was not addressed analytically is another reason why the HTDS report overstates the strength of conclusions with regard to the size of effect that may be present in light of the data” .
An Important Finding Overlooked
The [study] population also had a surprising amount of thyroid disease although its prevalence was not dose related. The overall incidence of almost
19 percent autoimmune thyroiditis with this number reaching 24 percent for women in the study is more than might be expected from results of normal population studies. The numbers for hypothyroidism (19% of the total population, 27.5 percent of the women) is also higher than one might expect from other epidemiological studies of presumably normal popula- tions [67, p. 6].
HTDS conclusions were focused entirely upon the lack of any correlation between estimates of the participants’ thyroid doses and the subsequent occurrence of thyroid illness. There was no recognition of the excess rates of thyroid disease found within the study group as compared with what would be expected from an unexposed group. Although the comparison of thyroid disease rates of HTDS participants to rates in other populations is made difficult due to the study’s protocol for thyroid screening, something that does not occur in other populations, the observation of excess occurrence of thyroid disease in the HTDS was not seriously considered when study conclusions were drawn.
The importance of attending to diverse and conflicting findings in epidemio- logical studies was emphasized by Alice Stewart, the epidemiologist who dis- covered the link between obstetric x-rays and childhood cancer:
The epidemiologist is like a conductor—you must hear every note, you must be able to detect a false note anywhere. If you hear a false note, you don’t send the violins away: you try to work with them. You must include all types of seemingly extraneous data in the collection process, it might be the key to unraveling a mystery. Handling the noise is the greatest thing in epidemiology [68, p. 216].
Had this been a thyroid disease prevalence study rather than a dose/incidence comparison, high prevalence of thyroid disease would have been found. As Stewart said, “The best way not to find something is not to look for it” [68, p. 193].
While looking at estimated dose and levels of thyroid disease among the study group, the HTDS found 20 thyroid cancers out of a participating study group of 3,441 (.58 percent). Based upon the amounts of I-131 released from Hanford, the Agency for Toxic Substances and Disease Registry had predicted that its medical monitoring program would find 90 thyroid cancers out of a study group of 14,000 (.64 percent) .
The Connecticut Tumor Registry (CTR) is the oldest population-based tumor registry in the country and is similar to the HTDS in that both require histo- logical confirmation of thyroid cancer diagnosis. There would be 5.3 cancers projected by the CTR for a group of 3,441 (probability of thyroid cancer,
0.00153983 × 3441 = 5.3). The ratio of observed cancer found by the HTDS is nearly four times the rate of residents in Connecticut.
Hypothyroidism occurs in approximately 2 percent of the population . The HTDS found 7.8 percent confirmed hypothyroid prevalence. Benign thyroid nodules occur in 2-4 percent of the general population. Over 7 percent prevalence was found in the HTDS. In the final HTDS report, under the “second alternative” of diagnosis, there were 297 cases of nodules (8.6 percent). Goiter and other disorders of the thyroid are reported to occur in 2.6 percent of the population, according to the National Health Interview Statistics data. The HTDS found autoimmune thyroiditis, alone, was 18.9 percent. Eight hundred and six (23.4 percent) were found to be antibody positive, although this was not dis- cussed in the summary report.
59. See Ruttenber, A. J., et al. 30 March 2004. A technical review of the final report of the Hanford Thyroid Disease Study. p. 3, citing Hoffman 1991, Hoffman et al., 1993, Hoffman et al., 1996, Hoffman 1999. Prepared as an expert report for the Hanford litigation, to respond to suggestions and recommendations of the NRC Subcom- mittee’s 2002 Hanford Thyroid Disease Study Draft Final Report. See also Hoffman, F. O., Ruttenber, A. J., Apostoaei, A. L., Carroll, R. J., and Greenland, S. 2007. The Hanford Thyroid Disease Study: An alternative view of the findings. Health Physics Journal 92(2):99-111.
a. HTDS results do not show statistically significant elevations in risk but are not inconsistent with other published studies supporting risks for certain thyroid diseases from I-131 exposures, if the upper bounds of the calculated confidence intervals are considered (as pointed out for the situation of thyroid cancer and I-131 exposure from NTS fallout by the NRC). [emphasis added]
b. Applying a strict interpretation of the lack of statistical significance found in the results of HTDS, we find that the results of HTDS are consistent with the finding of thyroid risk in some but not all studies of I-131 exposures, but not consistent with those studies which show elevated thyroid risk, or;
c. If the results are subjected to strict interpretation based upon statistical signifi- cance, then HTDS is not inconsistent with other studies which show that chronic exposure to I-131 is not associated with thyroid disease.
66. Greenland, S. 1977. Response and follow-up bias in cohort studies. American Journal of Epidemiology 106(3):184-187.
67. Fred Hutchinson Cancer Research Center/CDC. 1998. Preliminary technical review of the Hanford Thyroid Disease Study draft final report, p. 6.
68. Greene, G. 1999. The woman who knew too much: Alice Stewart and the secrets of radiation. Ann Arbor, MI: University of Michigan Press, p. 216.
69. The incidence of thyroid cancer found within HTDS was very close to that which was predicted by the medical monitoring program plan. See Spengler, R. F. July
1997. Hanford medical monitoring program: Background consideration document and ATSDR decision. US DHHS, ATSDR.
70. HTDS Newsletter, February 1997.