667 / 670
Table 2: Accuracy—Bias compared to reference material
Nominal %
Bias
T
stat
(4)
DF
(5)
p
-value
(6)
09 Dec 2015
10.9
14 Dec 2015
10.6
16 Dec 2015
11.0
21 Dec 2015
9.8
21 Dec 2015
9.4
29 Dec 2015
10.0
29 Dec 2015
9.7
31 Dec 2015
10.0
31 Dec 2015
9.5
05 Jan 2016
9.5
05 Jan 2016
9.9
07 Jan 2016
10.3
07 Jan 2016
10.6
Footnotes:
(1)
H
0
: = 0, The null hypothesis is that there is no difference between the measured results and the certified value:
(2)
k = coverage factor used for clculating expanded uncertainty. These are given in the NIST certificate, although it is often 2.
(3)
(4)
where: = mean of the differences between measured results and reference value
sd = standard deviation of the experimental results
n
= number of replicate analyses of SRM
U
CRV
= CRV uncertainty
(5)
DF was calculated using Satterthwaite approximation:
where: n
CRV
-1= DF
crv
= mean of the differences between measured results and certified value
s
m
= standard deviation of differences between measured results and certified value
n
m
= number of replicate analyses of CRM
U
CRV
= uncertainty of certified reference value
k = coverage factor used for calculating expanded uncertainty
(6)
p-value is he probability (at the stated level of confidence) of obtaining the test statistic assuming that the null hypothesis is true.
p
-value < 0.05 indicate a difference of statistical signifance between measured results and CRV.
NIST1849a
Vit D3
11.1
CRM
Product
Analyte
Certified
value
- 12.8
Certified Reference Material
Measured Results
(1)
Certified
range
k
(2)
2
Uncertainty
10.1
Results
(ug/hg)
DF
CRV
= calculated for k, using a 2-sided t distribution at
D
=0.05. An empirical model for doing this calculation was obtained by fitting 1/DF vs log t
0.05
to a 4th order polynomial for integral values of DF from 2-
100 DF. The maximum relative error over the fitted range was 0.06%.
Mean
SD
95%
Confidence
interval
Bias
9.8 - 10.4
-9.1%
1.165
63.92
0.25
0.53
1.7
9.4
60
DF
CRV
(3)
Date
d
n
t
crit
sd
d
d
d
SPIFAN ERP Checklist v1.0
VitD-18 (February 2016)
FOR ERP USE ONLY
DO NOT DISTRIBUTE