604-605 / 620
Table 2
Nominal
T
stat
p
-value
125.6
0.1
128.5
-2.8
128.7
-3.0
128.8
-3.1
130.3
-4.6
130.0
-4.3
131.2
-5.5
136.4
-10.7
122.5
3.2
122.4
3.3
127.4
-1.7
130.2
-4.5
Mean
128.5
-2.8
SD
3.8
3.8
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
2.8
- 130.9
2.545
0.027
126.1
Bias
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
Confidence interval
SRM 1849a
Thiamin (ug/100g)
125.7
9.8
115.9 - 135.5
n
/
sd
d
d
d
n
t
crit
sd
n
t
crit
sd
crit
t
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