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Table 2: Accuracy—Bias compared to reference material

Nominal %

Bias

T

stat

(4)

DF

(5)

p

-value

(6)

09 Dec 2015

10.9

14 Dec 2015

10.6

16 Dec 2015

11.0

21 Dec 2015

9.8

21 Dec 2015

9.4

29 Dec 2015

10.0

29 Dec 2015

9.7

31 Dec 2015

10.0

31 Dec 2015

9.5

05 Jan 2016

9.5

05 Jan 2016

9.9

07 Jan 2016

10.3

07 Jan 2016

10.6

Footnotes:

(1)

H

0

: = 0, The null hypothesis is that there is no difference between the measured results and the certified value:

(2)

k = coverage factor used for clculating expanded uncertainty. These are given in the NIST certificate, although it is often 2.

(3)

(4)

where: = mean of the differences between measured results and reference value

sd = standard deviation of the experimental results

n

= number of replicate analyses of SRM

U

CRV

= CRV uncertainty

(5)

DF was calculated using Satterthwaite approximation:

where: n

CRV

-1= DF

crv

= mean of the differences between measured results and certified value

s

m

= standard deviation of differences between measured results and certified value

n

m

= number of replicate analyses of CRM

U

CRV

= uncertainty of certified reference value

k = coverage factor used for calculating expanded uncertainty

(6)

p-value is he probability (at the stated level 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 CRV.

NIST1849a

Vit D3

11.1

CRM

Product

Analyte

Certified

value

- 12.8

Certified Reference Material

Measured Results

(1)

Certified

range

k

(2)

2

Uncertainty

10.1

Results

(ug/hg)

DF

CRV

= calculated for k, using a 2-sided t distribution at

D

=0.05. An empirical model for doing this calculation was obtained by fitting 1/DF vs log t

0.05

to a 4th order polynomial for integral values of DF from 2-

100 DF. The maximum relative error over the fitted range was 0.06%.

Mean

SD

95%

Confidence

interval

Bias

9.8 - 10.4

-9.1%

1.165

63.92

0.25

0.53

1.7

9.4

60

DF

CRV

(3)

Date

d

n

t

crit

sd

d

d

d

SPIFAN ERP Checklist v1.0

VitD-18 (February 2016)

FOR ERP USE ONLY

DO NOT DISTRIBUTE