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HTDS Guide > How the Study
Was Conducted > Study Group Selection
HTDS Guide
| How the Study Was Conducted |
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Study Group Selection
The HTDS study population represents a sampling of people born
between 1940 and 1946 to mothers who lived in seven counties in
Washington State: Benton, Franklin, Adams, Walla Walla, Okanogan, Ferry
and Stevens.
All of the participants were young children at the time of the
largest radiation releases from Hanford. It is believed that young
children receive a higher dose to the thyroid for the same level of
exposure than do adolescents and adults, and that the thyroid gland in
young children may be more sensitive to the effects of radiation.
The study participants represent a range of possible doses of
iodine-131 from Hanford, from the highest doses to very low doses.
Starting from birth certificates of 5,199 people born between 1940
and 1946, investigators were able to locate 94 percent of the group
(4,350 people still living and 527 deceased). Of these, 3,440 were
willing and able to participate fully.
Of the 3,440 study participants, 249 moved out of the Hanford region
before Hanford operations began and did not move back into the region
any time before the end of 1957. They are referred to as "out of area"
participants in the HTDS. Because their thyroid doses could not be
estimated with the computer models used by the HTDS, out of area
participants were included in the data analyses as a separate group (see
Figures 1-4 in Findings and Interpretations).
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