3.3. Homogeneity
Homogeneity was assessed for the two spiked candidate refer-
ence materials B (very low level) and C (low level) using the Euro-
pean Screening Method with the VIDAS SET2 assay as detection
step. The data acquired was first assessed for the presence of out-
liers. Neither the filling sequence (sample means of the 10 units
analysed in triplicate) nor the analytical sequence (individual mea-
surements in chronological order) revealed outliers for any mate-
rial. Individual data and bottle means showed normal or
unimodal distribution. Consequently, an uncertainty contribution
from possible heterogeneity was estimated according to Linsinger
et al. (2001) by an analysis of variance (ANOVA). No trends were
detected for the filling and analytical sequences for both materials
(Fig. 1). Results are summarized in Table 3. The larger standard