444-445 / 620
Table 2
Nominal
T
stat
p
-value
15.4
-0.3
15.8
-0.7
15.4
-0.3
15.8
-0.7
15.6
-0.5
15.2
-0.1
15.2
-0.1
15.3
-0.2
14.7
0.4
Mean
15.4
-0.3
SD
0.3
0.3
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
15.1 - 15.6
Bias
Confidence interval
0.3
2.437
0.041
SRM 1849a
Zn (mg/100g)
15.1
0.56
14.54 - 15.66
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
n
/
sd
d
d
d
n
t
crit
sd
n
t
crit
sd
crit
t
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