Table 2
Accuracy -
SRM Product
Code
Analyte
Reference
value
1
Measured value
Bias
(mg/kg pwd)
Conc. (mg/kg pwd)
T
stat
p
-value Confidence Interval
0.0420
0.0437
0.0443
0.0423
0.0430
-
0.0420
0.0419
0.0420
0.0401
1. Approximately 50% of the data used to determine the NIST vitamin B12 reference value were generated with the microbiological method which is known to be biased high.
T
stat
=
where: = mean of the differences between measured results and reference value
sd = standard deviation of the differences between results and reference value
n
= number of replicate analyses of SRM
H
0
: = 0, The null hypothesis is that there is no difference between the measured results and the certified value:
p
-value: is the probability (at the 95% levels 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 SRM.
95% confidence interval: The true population of the measured value expected to fall within the confidence interval estimate 95% of the time.
lower limit = mean
-
upper limit = mean +
where: = critical values of the t-distribution
sd = standard deviation of the differences between results an reference value
n
= number of replicate analyses of SRM
0.00000051
0.0414
0.0433
1849a
Vitamin B12
0.0482
-14.483
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