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Figure 20: Plotted raw data for NIST 1869 CRM powder (fortified)
Method Precision
The submitted data was statistically analysed using the AOAC protocol for overall mean, intra-laboratory
repeatability (S
r
), repeatability relative standard deviation (RSD
r
), inter-laboratory reproducibility (S
R
),
reproducibility relative standard deviation (RSD
R
), and HorRat (2). Cochran (p = 0.025, 1-tail) and Grubbs
(single and double, p = 0.025, 2-tail) tests were utilized to determine outliers (3,4). The statistical analysis of
results submitted by participants is given in Table 2 with pertinent values for method illustrated in Figures
21–23. Only a single pair of results for vitamin D
2
(samples GBAN911/PTLO721) from Lab 6 were excluded
as Cochran outliers, no other outliers were identified and all other results were used in the generation of
precision values.
Precision as repeatability ranged from 1.9–5.8% RSD
r
and reproducibility values ranged from 6.4–12.7%
RSD
R
. For all vitamin D fortified products, the repeatability and reproducibility are within limits set in the
Vitamin D SMPR (2). Acceptable reproducibility was also demonstrated with better than expected HorRat
R
values for the method ranging from 0.2–0.6 (expected range 0.5–2.0) (4).
0.0
5.0
10.0
15.0
20.0
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Vitamin D
2
(μg hg
-1
)
Lab Number
Sample GBAN911/PTLO721
2016.05 (FEBRUARY 2017) VITD-18
MLT REPORT
FOR ERP USE ONLY
DO NOT DISTRIBUTE