504-505 / 620
Table 2
Nominal
T
stat
p
-value
12.9
0.6
13.6
-0.1
13.9
-0.4
12.9
0.5
13.4
0.1
12.9
0.6
13.0
0.5
13.3
0.2
13.0
0.5
Mean
13.2
0.3
SD
0.4
0.4
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
SRM1849a
Pyridoxine
13.46
0.93
12.53 - 14.39
Certified range
12.9 - 13.5
Bias
Confidence interval
-0.3
2.238
0.056
Accuracy - Analytical bias compared to reference material
Certified Reference Material
Measured Results
CRM product
Analyte
Certified value Uncertainty
Concentration
Difference from
certified value
n
/
sd
d
d
d
n
t
crit
sd
n
t
crit
sd
crit
t
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