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Table 2

Nominal

T

stat

p

-value

990

90.1

987

92.8

1041

38.8

1004

76.0

1074

6.3

1067

13.3

1079

1.4

1117

-37.3

979

100.9

977

103.1

1030

49.8

1012

68.5

Mean

1029.7

50.3

SD

46.0

46.0

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

Niacin (ug/100g)

1080

100

980 - 1180

1000.5 - 1058.9

Bias

Confidence interval

-50.3

3.792

0.003

n

/

sd

d

d

d

n

t

crit

sd

n

t

crit

sd

crit

t

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