384-385 / 620
Table 2
Nominal
T
stat
p
-value
7394.8
-384.8
7457.8
-447.8
7468.1
-458.1
7449.8
-439.8
7616.7
-606.7
7750.6
-740.6
7453.5
-443.5
7458.7
-448.7
7472.3
-462.3
Mean
7502.5
-492.5
SD
110.3
110.3
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
- 7587.3
SRM 1849a
Chloride
7010
7010 - 7010
13.389
0.000
7417.7
492.5
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
Bias
n
/
sd
d
d
d
n
t
crit
sd
n
t
crit
sd
crit
t
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