502-503 / 620
Table 2
Nominal
T
stat
p
-value
105.0
3.1
110.5
-2.5
103.3
4.7
106.5
1.5
106.6
1.4
108.5
-0.5
102.4
5.6
107.9
0.1
108.5
-0.5
Mean
106.6
1.4
SD
2.6
2.6
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
Nicotinamide
108
10
98 - 118
Certified range
104.6 - 108.6
Bias
Confidence interval
-1.4
1.632
0.141
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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