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Table 2

Nominal

T

stat

p

-value

106

1.2

103

4.2

107

0.2

107

0.2

108

-0.8

103

4.2

103

4.2

104

3.2

101

6.2

Mean

104.7

2.5

SD

2.4

2.4

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

102.8 - 106.5

Bias

Confidence interval

-2.5

3.169

0.013

SRM 1849a

Cr (µg/100g)

107.2

3.2

104 - 110.4

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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