352-353 / 620
Table 2
Nominal
T
stat
p
-value
142.2
-6.2
141.8
-5.8
138.1
-2.1
138.6
-2.6
134.7
1.3
128.3
7.7
129.7
6.3
135.5
0.5
126.3
9.7
Mean
135.0
1.0
SD
5.8
5.8
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
SRM 1849a
Free Carnetine
136
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
- 139.5
14
122 - 150
0.505
0.627
130.6
-1.0
n
/
sd
d
d
d
n
t
crit
sd
n
t
crit
sd
crit
t
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