IJCA Vol 5 Issue 1 - Flipbook - Page 45
2026 | Volume 5, Issue 1
The International Journal of Conformity Assessment
approach depends on factors such as the number
of participants and the availability of independent
references.
Calibration comparisons often involve limited
numbers of participants, including bilateral or
small-group ILCs. In such cases, meaningful
performance evaluation remains possible when
assigned values and associated uncertainties
are well characterized and acceptance criteria
are defined in advance. ISO 13528 also cautions
against drawing performance conclusions when
assigned-value uncertainty is too large to support
meaningful assessment.
7. Use of Interlaboratory Comparisons
Other Than Pro昀椀ciency Testing
Although proficiency testing is a primary
mechanism for demonstrating laboratory
competence, formal PT schemes are not always
available or technically appropriate for all
calibration activities. Accreditation frameworks
therefore allow the use of interlaboratory
comparisons other than proficiency testing,
provided their selection and implementation are
justified and documented.
ILAC-P9 explicitly recognizes that suitable PT
schemes may not exist for certain measurands
or scopes. In such cases, laboratories may rely
on alternative ILCs to support monitoring of
measurement validity, provided these activities
are planned, technically sound, and aligned with
accreditation expectations.
7.1 Conditions for Acceptance of Non-PT ILCs
Unlike formal PT schemes, alternative ILCs may
not include standardized scoring or classification
of participant performance. Nevertheless, they
must be designed to provide meaningful evidence
of technical competence. Key considerations
include the establishment of an assigned value,
definition of acceptance criteria, and evaluation of
results relative to measurement uncertainty.
Accreditation bodies expect laboratories to justify
the use of non-PT ILCs on a technical basis. This
justification should be specific to the measurand
and scope involved and should explain why
formal PT is unavailable or inappropriate. General
statements regarding lack of PT availability are
insufficient without supporting evidence.
7.2 Evaluation and Documentation Requirements
For non-PT ILCs to be acceptable, laboratories
must document how results were evaluated
and how conclusions were reached. Even when
formal PT performance scores are not applied,
the principles of metrological compatibility
remain relevant. Results should be assessed to
determine whether they are consistent within
combined uncertainties and whether any observed
discrepancies warrant investigation.
Documentation should include evidence of
searches for available PT schemes, description
of the comparison design, identification of
assigned values and associated uncertainties,
evaluation criteria, and interpretation of results.
Where non-PT ILCs are used on a recurring basis,
laboratories should periodically reassess whether
formal PT schemes have become available or
whether changes in scope or capability affect the
suitability of the approach.
7.3 Role of Non-PT ILCs Within a Risk-Based
Framework
Alternative interlaboratory comparisons should be
integrated into the laboratory’s overall risk-based
PT/ILC participation strategy rather than treated
as ad hoc substitutes. When selected deliberately
and documented appropriately, they can support
validation of measurement uncertainty and
provide supplementary evidence of technical
competence.
However, reliance on non-PT ILCs does not
eliminate the obligation to participate in formal
PT schemes when they become available and
appropriate. Laboratories are expected to remain
aware of PT availability and to update participation
plans accordingly. Within this framework, non-PT
ILCs function as complementary tools rather than
permanent replacements for proficiency testing.
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