606-607 / 620
Table 2
Nominal
T
stat
p
-value
234.0
-30.3
220.5
-16.8
230.1
-26.4
222.5
-18.8
236.4
-32.7
235.6
-31.9
235.2
-31.5
244.4
-40.7
210.1
-6.4
210.6
-6.9
220.6
-16.9
224.8
-21.1
Mean
227.1
-23.4
SD
10.7
10.7
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
Riboflavin (ug/100g)
203.7
5.2
198.5 - 208.9
220.3 - 233.9
Bias
Confidence interval
23.4
7.579
0.000
n
/
sd
d
d
d
n
t
crit
sd
n
t
crit
sd
crit
t
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