538-539 / 620
Table 2
Nominal
T
stat
p
-value
990
90.1
987
92.8
1041
38.8
1004
76.0
1074
6.3
1067
13.3
1079
1.4
1117
-37.3
979
100.9
977
103.1
1030
49.8
1012
68.5
Mean
1029.7
50.3
SD
46.0
46.0
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
Niacin (ug/100g)
1080
100
980 - 1180
1000.5 - 1058.9
Bias
Confidence interval
-50.3
3.792
0.003
n
/
sd
d
d
d
n
t
crit
sd
n
t
crit
sd
crit
t
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