SAMPLE HETEROGENEITY
T
100 F176,
—
e
—
=
a
U
a.
T
T
I
7
5
f°
=
#3
i
“
PT
T
T
=
T_
f
T
T
Tf
q
~»
T
Po
ood
—
&
°
oO
5 og
—-d
a
0
—
4
|
L
j
|
i
l
|
|
|
{
|
T
T
TTT
T
I
|
T
T
T
T
I
4
7
a
5,
=
S10 FIE
'
Qa
|
DE
t
oC
Og
f
g
T
bon
fen
=
50 |
0
T
719
°
%
°
*
g
°
°
°
o
3
4
=
Oo
°
—
7
—
oC
|
L
i
l
I
l
l
|
i
t
|
L
|
i
7]
MAY JUN JUL AUG SEP OCT NOV DEC|JAN FEB MAR APR MAY JUN JUL AUG
1962
1963
Fig. 9—Distribution of the mean concentrations of 1’Cs and Sy in
evening milk. Composite samples from a herd of 17 to 24 cous.
period of one year. In this interval the diet of the cattle changed six
times because of the feeding of hay grown in different seasons of the
year. The deposition of fallout changed while each cutting of alfalfa was
growing, and the rates of growth varied simultaneously, as shewIn
Figs. 7 and 8. Individual cows began and terminated lactation periods,
thereby varying the volume of iilk pioduced daily. Differences in the
metabolic efficiency among cows in extracting Sr and Bicg from feeds
also contributed to daily variability.
The high cost of radiochemical determinations precludes dissipating analytical resources on objectives that cannot be achieved with pre-
cision. Ascertaining whether a particular objective Should be attempted
necessitates that estimates be made of the size of sample required to
obtain the precision desired within a Specified confidence interval.
Therefore, since this was an exploratory study, only small samples of
six to eight specimens were analyzed for "Sr and "Cs. Their means
and standard deviations were used to estimate sample requirements for
defining fission-product concentrations in different materials on the
farm. The weights of the specimens in a sample were used to estimate
the size of the sample needed to determine the quantities of the different materials.
The population parameter needed for reliable estimates of sample
size is the population standard deviation.? This parameter was not
available. However, the sample standard deviations can be used with