540-541 / 620
Table 2
Nominal
T
stat
p
-value
131.7
2.9
134.1
0.5
129.9
4.7
130.5
4.1
129.7
4.9
126.2
8.4
143.3
-8.7
144.3
-9.7
130.4
4.2
129.3
5.3
129.5
5.1
128.6
6.0
Mean
132.3
2.3
SD
5.7
5.7
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
Accuracy - Analytical bias compared to reference material
Certified Reference Material
Measured Results
CRM product
Analyte
Certified value Uncertainty Certified range Concentration
Difference from
certified value
SRM 1849a
Pyridoxine (ug/100g)
134.6
9.3
125.3 - 143.9
128.7 - 135.9
Bias
Confidence interval
-2.3
1.406
0.187
n
/
sd
d
d
d
n
t
crit
sd
n
t
crit
sd
crit
t
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