172
10 Interlaboratory Comparisons
quality of the obtained results. Depending on the results obtained, participation in the
ILC/PT can confirm high competencies of the laboratory in the scope of the specific
testing. In cases where the results show any doubt, it can be a tool supporting the critical analysis of the potential problems. In principle, the participation of a laboratory
in ILC can be voluntary, but there are some situations when it can be enforced by specific requirements (legal, accreditation, request from customer). In all cases where
the evaluation of result is unsatisfactory, the laboratory should consider the cause
of obtaining questionable or unsatisfactory results. This reason could arise from the
systematic influence not being taken into consideration (e.g., incomplete recovery
during extraction) or that that not all of the uncertainty components were considered
during evaluation. Therefore, participation in interlaboratory comparisons should be
considered as a meaningful tool allowing for the identification of problems. Thus,
the critical evaluation of the results of ILC/PT supports all activities towards valid
corrective actions.
In order to make the ILC/PT schemes useful for participating laboratories, the
ILC/PT provider should use the well-defined and transparently described statistical
procedure including the information on how the data will be processed and how
the laboratory performance will be evaluated. This should also include information
on how the assigned value/values for individual parameters will be assigned. The
requirements for the ILC/PT providers are well described in ISO/IEC 17043, and the
information on the statistical uses for the evaluation of laboratory results is discussed
in ISO 13528.
A number of various approaches are known and are used to define the assigned
value as well as the target range. This is essential, since the performance of individual
laboratories is evaluated with scores, which are based on the comparison of laboratory
results with an assigned value, dominated by the target range. In practice, various
scoring systems are used, each with a specific evaluation criteria; thus is worthwhile
to understand the idea behind the criteria.
The assigned value can be described in several ways, for example: based on
formulation; as a certified reference value; and agreed as a consensus value.
Participation of laboratory in interlaboratory comparison.
Assessing the technical competencies of the laboratory, based on the result of the
participation in ILC/PT, it should be evaluated whether the type of samples and
applied measuring procedure correspond to the scope of measurements carried out
in the laboratory. It rarely happens that a laboratory conducts measurements for one
type of object only. Most often, the scope is diverse and encompasses various objects;
their different properties are tested and various analytical techniques are used. Hence,
it is important for the laboratory to skillfully gather those measuring procedures that
can be evaluated with one type of interlaboratory comparison/proficiency testing.
The detailed information regarding the specific requirements is given in the EA4/18:2010 ‘Guidance on the Level and Frequency of Participation in Proficiency
Testing.’ In the document, the choice of subdisciplines is also emphasized.
10 Interlaboratory Comparisons
quality of the obtained results. Depending on the results obtained, participation in the
ILC/PT can confirm high competencies of the laboratory in the scope of the specific
testing. In cases where the results show any doubt, it can be a tool supporting the critical analysis of the potential problems. In principle, the participation of a laboratory
in ILC can be voluntary, but there are some situations when it can be enforced by specific requirements (legal, accreditation, request from customer). In all cases where
the evaluation of result is unsatisfactory, the laboratory should consider the cause
of obtaining questionable or unsatisfactory results. This reason could arise from the
systematic influence not being taken into consideration (e.g., incomplete recovery
during extraction) or that that not all of the uncertainty components were considered
during evaluation. Therefore, participation in interlaboratory comparisons should be
considered as a meaningful tool allowing for the identification of problems. Thus,
the critical evaluation of the results of ILC/PT supports all activities towards valid
corrective actions.
In order to make the ILC/PT schemes useful for participating laboratories, the
ILC/PT provider should use the well-defined and transparently described statistical
procedure including the information on how the data will be processed and how
the laboratory performance will be evaluated. This should also include information
on how the assigned value/values for individual parameters will be assigned. The
requirements for the ILC/PT providers are well described in ISO/IEC 17043, and the
information on the statistical uses for the evaluation of laboratory results is discussed
in ISO 13528.
A number of various approaches are known and are used to define the assigned
value as well as the target range. This is essential, since the performance of individual
laboratories is evaluated with scores, which are based on the comparison of laboratory
results with an assigned value, dominated by the target range. In practice, various
scoring systems are used, each with a specific evaluation criteria; thus is worthwhile
to understand the idea behind the criteria.
The assigned value can be described in several ways, for example: based on
formulation; as a certified reference value; and agreed as a consensus value.
Participation of laboratory in interlaboratory comparison.
Assessing the technical competencies of the laboratory, based on the result of the
participation in ILC/PT, it should be evaluated whether the type of samples and
applied measuring procedure correspond to the scope of measurements carried out
in the laboratory. It rarely happens that a laboratory conducts measurements for one
type of object only. Most often, the scope is diverse and encompasses various objects;
their different properties are tested and various analytical techniques are used. Hence,
it is important for the laboratory to skillfully gather those measuring procedures that
can be evaluated with one type of interlaboratory comparison/proficiency testing.
The detailed information regarding the specific requirements is given in the EA4/18:2010 ‘Guidance on the Level and Frequency of Participation in Proficiency
Testing.’ In the document, the choice of subdisciplines is also emphasized.