466-467 / 620
Table 2
Nominal
T
stat
p
-value
19.5
0.3
19.8
0.0
19.3
0.5
19.3
0.5
19.6
0.2
20.1
-0.3
20.1
-0.3
20.1
-0.4
19.4
0.4
Mean
19.7
0.1
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
Analyte
Average concentration
mg/kg
Certified value
mg/kg
Bias (%)
Uncertainty
mg/kg
R% Low High
Ca
5148
5253
98.0
51
6
4938
5568
Cu
19.69
19.78
99.6
0.26
10
17.80 21.76
Fe
167.0
175.6
95.1
2.9
10
158.0 193.2
K
9502
9220
103.1
110
6
8667
9773
Mg
1566
1648
95.0
36
9
1500
1796
Mn
48.74
49.59
98.3
0.97
10
44.63 54.55
Na
4244
4265
99.5
83
6
4009
4521
P
4086
3990
102.4
140
6
3751
4229
Zn
146.8
151.0
97.2
5.6
10
135.9 166.1
Bias
Accuracy - Analytical bias compared to reference material
Certified Reference Material
Measured Results
CRM product
Analyte
Certified value
0.26
19.52 - 20.04
0.747
SRM1849a
Cu
19.78
0.476
19.4
-0.1
Uncertainty Certified range Concentration
Difference from
certified value
Confidence interval
- 20.0
n
/
sd
d
d
d
n
t
crit
sd
n
t
crit
sd
crit
t
SPIFAN ERP Checklist v1.0