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Table 2

Nominal

T

stat

p

-value

234.0

-30.3

220.5

-16.8

230.1

-26.4

222.5

-18.8

236.4

-32.7

235.6

-31.9

235.2

-31.5

244.4

-40.7

210.1

-6.4

210.6

-6.9

220.6

-16.9

224.8

-21.1

Mean

227.1

-23.4

SD

10.7

10.7

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

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

SRM 1849a

Riboflavin (ug/100g)

203.7

5.2

198.5 - 208.9

220.3 - 233.9

Bias

Confidence interval

23.4

7.579

0.000

n

/

sd

d

d

d

n

t

crit

sd

n

t

crit

sd

crit

t

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