410-411 / 620
Table 2
Nominal
T
stat
p
-value
212.4
-1.4
214.6
-3.6
190.4
20.6
197.8
13.2
206.1
4.9
205.4
5.6
210.4
0.6
209.6
1.4
193.6
17.4
195.2
15.8
190.3
20.7
195.4
15.6
205.2
5.8
201.7
9.3
Mean
202.0
9.0
SD
8.2
8.2
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
SRM 1849
Folic acid
211
Bias
Accuracy - Analytical bias compared to reference material
Certified Reference Material
Measured Results
CRM product
Analyte
Certified value
(mcg/100 g)
Uncertainty
(mcg/100 g)
Certified range
(mcg/100 g)
Concentration
(mcg/100 g)
Difference from
certified value
Confidence interval
(mcg/100 g)
- 206.8
13
198 - 224
4.082
0.001
197.2
-9.0
n
/
sd
d
d
d
n
t
crit
sd
n
t
crit
sd
crit
t
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