In the population of Utirik (158 persons, all ages) followed for
21 years, the accumulated person-years of observation are estimated at
405708
3140. In such a group, expection of thyroid cancer would be as follows:
(1)
Based on an average for all registries listed in "Cancer
Incidence on Five Continents" (2.5/100,000 per year):
.08 cases, upper 95% confidence limit .66
(2}
Based on incidence rates in the Marshal Islands,
‘
a lagen
meW-/429 \}
4,
(dates),
excluding cases in exposed individuals (2.0/100,000 per year):
.06 cases, upper 95% confidence limit .54
(3)
Based on estimates of the risk per rad thyroid dose per year
observed in Rongelap and Ailingnae combined (3.9/1,000,000/
:
Oo
|
-
|
rad/year, person~yoarseat~riskrest-3140, thyroid dose 50 rads j=
157,000 person-rad-years) :
-61 cases, upper 95% confidence limit 2.17
~~
J
:
A c Conclusions:
0
,
4
3 q
1),
(1)
~ 5
unlikely to be due to chance at conventional levels of statis-
UL 3 a
tical significance - if the rates do not exceed normal
; Ue
population rates. The occurrence of 2 cases by chance is extremely
C
Qi= ~
unlikely.
) iy 3%
¢
<3
&
iz
o
E
8
The occurrence of even 1 case of thyroid cancer in Utirik is
,
.
,
;
oo
po
Zz
=
-
a
(2)
an
os
The observed number of thyroid cancers is higher than would be
,
:
expected on the basis of experience in the exposed populations
.
.
teat
$
. oo
.
7
.
.
‘
of Rand A, but does not exceed the upper 95% confidence limit
i 39 §
28
8
-
of the expected value.
:
Caveats
(1)
In computing expected values, no account has been taken of age
and
sex differences between populations. The incorporation of
i
|
Vorique
adjustments for these factors is unlikely to change the above
conclusions.