Information about the content of the assessment report/calibration certificate when a laboratory has to state compliance with specifications
(based on ILAC-G8:03/2009, Guidelines on the Reporting of Compliance with Specification)
The information is intended for assessors of the Accreditation Body of Serbia and laboratories that need to provide statements of compliance with specifications in their test reports/calibration certificates.
The following references from ILAC-G8:03/2009, Guidelines on the Reporting of Compliance with Specification enable/explain coherent application of specific requirements of SRPS ISO/IEC 17025:
- For testing laboratories, ISO/IEC 17025:2005 (clause 220.127.116.11 b) requires that “the test report shall, where necessary for the interpretation of the test results include…, where relevant, a statement of compliance/non-compliance with requirements and/or specification”.;
- For calibration laboratories, ISO/IEC 17025:2005 (clause 18.104.22.168) requires that “if a statement of compliance with a specification is made, this shall identify which clauses of the specification are met or not met”. It is permissible to omit the measurement result and its uncertainty from the report as long as they are retained for possible future reference.
Statements of compliance with requirements and/or specifications shall not be considered opinions or interpretations in terms of SRPS ISO/IEC 17025. Therefore, when a laboratory reports such compliance in its test reports/calibration certificates, it has to be properly defined (e.g. statement of compliance with specification, conclusion, etc, but not “opinion”, “interpretation” or “opinion and interpretation”).
When laboratories provide statements of compliance with requirements and/or specifications in their test reports/calibration certificates, these test reports/calibration certificates shall, among other things, contain the following:
- Test/calibration results with expanded uncertainty;
- Coverage probability for expanded uncertainty;
- A statement of compliance should not be reported in a way where it could be confused with inspection or product certification and it can only pertain to a test/calibration item, and
- Source of specification.
When a specification describes an interval with an upper and lower limit, a statement of compliance or non-compliance should only be made where the ratio of the expanded uncertainty interval to the specified interval is reasonably small and fit for purpose (meaning that the laboratory should be able to meet the needs of the customer).
Measurement results can be stated without measurement uncertainty only when a specification or legal requirements require so (e.g. when it is stated that measurement uncertainty has been accounted for when setting the limits).
Stating compliance with specification for a single quantity
When a measurement result, including extended uncertainty, is compared with the specification interval (upper and lower specification limit) 4 cases can be defined (Figure 1):
- Case 1: measurement result with expanded uncertainty is below the upper specification limit or above the lower specification limit;
- Case 2: measurement result is below the upper specification limit or above the lower specification limit, but the interval of expanded uncertainty is outside the specification limit;
- Case 3: measurement result is above the upper specification limit or below the lower specification limit, but the interval of expanded uncertainty includes part of the specification interval;
- Case 4: measurement result with expanded uncertainty is above the upper specification limit or below the lower specification limit.
Figure 1. Compliance with specification for upper and lower limits
In case 1 compliance with the specification can be stated as “Compliance” or “Compliance – The measurement result is within (or below) the specification limit when the measurement uncertainty is taken into account with a 95% coverage probability for extended uncertainty”.
In case 4 noncompliance with the specification can be stated as “Non-compliance – The measurement result is outside (above upper or below lower) the specification limit when the measurement uncertainty is taken into account with a 95% coverage probability”.
In cases 2 and 3 it is not possible to state compliance or non-compliance. In Case 2 it is possible to indicate “It is not possible to state compliance using a 95 % coverage probability for the expanded uncertainty although the measurement result is below the upper limit”. Only in case of a clear need for the statement of compliance/noncompliance (e.g. legal requirement), case 2 can be reported as follows “Compliance – compliance cannot be confirmed with a 95 % coverage probability for expanded uncertainty which means that the measurement result can be outside (above upper or below lower) the specification limit”, while in case 3 this can be reported as “Noncompliance – noncompliance cannot be confirmed with a 95 % coverage probability for expanded uncertainty which means that the measurement result can be inside (below upper or above lower) the specification limit”.
In case of a measurement result that is equal to the specification limit the procedure will follow that of case 3. If a laboratory is using a coverage probability other than a 95% coverage probability, then a statement of compliance/noncompliance with specification has to be harmonised given the used coverage probability.
Stating compliance with specification involving multiple quantities
If the evaluation of compliance with specification comprises more quantities, each measurement value should be evaluated independently. The result of each evaluation should be reported.
An overall evaluation of compliance with requirements or specification may be formulated in one of the following ways, or by combining them:
- “All measured values comply with the specification limit(s)” or “The item/sample complies with the requirements”. This covers situations where all measurements comply with specification (Case 1 of Fig.1);
- “For some of the measured values it is not possible to make a statement of compliance with specification”. This covers situations where some of the measurements demonstrate neither compliance nor non-compliance with specification (Case 2 and 3 of Fig.1).
- “Some of the measured values do not comply with specifications” or “The item/sample does not comply with the requirements”. This covers situations where one or more measurements are in non-compliance with specifications (Case 4 of Fig.1).