182
10 Interlaboratory Comparisons
laboratories. This allows the laboratory performance to be evaluated with regard the
expected use of the result.
In the case, when the reference value is determined with the primary method, for
example ID ICP MS (Isotopic Dilution Inductively Coupled Plasma Mass Spectrometry), the uncertainty assigned to the reference value is very small. In laboratories
working in the area of the environmental analysis, a higher uncertainty is most often
satisfactory, hence it was decided that taking into consideration the uncertainty provided by the laboratory would ensure a more reliable method of evaluation.
10.12.2 Indicators of the Evaluation of Laboratories
Participating in Interlaboratory Comparisons
z
(x − X odn )
σ p
z
(x − X odn )
σ 2
p + u
2
X
zeta
x − X odn
u 2
x + u
2
X
E n
x − X odn
U 2
x + U
2
X
10.13 Summary
The evaluation criteria used in ILC/PT allow the evaluation of the performance of a
single laboratory, whether or not it meets the preset criteria in respect of the reported
results. The evaluation scores z and z
do not include the uncertainty of the result
reported by the given laboratory, whereas zeta and E n scores accommodate it in the
denominator of respective equations.
Obtaining satisfactory performance with z and z
-scores (at the same time) means
that the laboratory meets the requirements set by the organizer of ILC/PT; obtaining a
satisfactory performance of the zeta and E n scores means that the laboratory meets its
own criteria. Various situations, when using z-score and zeta score are summarized
in Table 10.2, showing the evaluation criteria in practice.
10 Interlaboratory Comparisons
laboratories. This allows the laboratory performance to be evaluated with regard the
expected use of the result.
In the case, when the reference value is determined with the primary method, for
example ID ICP MS (Isotopic Dilution Inductively Coupled Plasma Mass Spectrometry), the uncertainty assigned to the reference value is very small. In laboratories
working in the area of the environmental analysis, a higher uncertainty is most often
satisfactory, hence it was decided that taking into consideration the uncertainty provided by the laboratory would ensure a more reliable method of evaluation.
10.12.2 Indicators of the Evaluation of Laboratories
Participating in Interlaboratory Comparisons
z
(x − X odn )
σ p
z
(x − X odn )
σ 2
p + u
2
X
zeta
x − X odn
u 2
x + u
2
X
E n
x − X odn
U 2
x + U
2
X
10.13 Summary
The evaluation criteria used in ILC/PT allow the evaluation of the performance of a
single laboratory, whether or not it meets the preset criteria in respect of the reported
results. The evaluation scores z and z
do not include the uncertainty of the result
reported by the given laboratory, whereas zeta and E n scores accommodate it in the
denominator of respective equations.
Obtaining satisfactory performance with z and z
-scores (at the same time) means
that the laboratory meets the requirements set by the organizer of ILC/PT; obtaining a
satisfactory performance of the zeta and E n scores means that the laboratory meets its
own criteria. Various situations, when using z-score and zeta score are summarized
in Table 10.2, showing the evaluation criteria in practice.