What is proficiency testing?
Proficiency testing is the use of interlaboratory test comparisons to determine
the performance of individual laboratories for specific tests or calibrations and
to monitor the consistency and comparability of a laboratory's test or calibration
data. One of the main uses of Proficiency Testing Schemes (PTS) is to assess laboratories'
ability to perform tests competently. It thus supplements laboratories' own internal
quality control procedures by providing an additional external evaluation of their
test capabilities. These activities also complement the technique of on- site laboratory
assessment by technical experts usually used by laboratory accreditation bodies
or other regulatory authorities. Confidence, that a testing or calibration laboratory
consistently obtains reliable results is of major importance to users of laboratory
services. Users seeking such an assurance may undertake their own evaluation or
may use the evaluation of other professional bodies. Bodies assessing the technical
competence of testing laboratories normally require or expect satisfactory participation
in proficiency testing as evidence of a laboratory' ability to produce reliable
test results, except where proficiency testing is inappropriate.
Aims of proficiency testing
- Check the consistency and comparability of data for individual testing/calibration
personnel;
- Assist in maintaining the calibration of instruments;
- Establish the effectiveness and comparability of new test methods;
- Achieve commercial improvement, through providing additional confidence to laboratory
clients;
- Achieving confidence in testing performance of accredited laboratories;
- Demonstration of competence in a testing field;
- Assist in determining reasons for interlaboratory differences;
- Determine the precision of a test method- often known as interlaboratory studies,
collaborative trials, or round- robins; This type is used when a new standard should
become effective, and it is not known, which differences in the results must be
expected. Often it becomes clear during this type of comparison test that part of
the new standard are not practical or not precise enough.
- Assign values to certified reference materials (CRMs) : In this case usually pre-
selected laboratories with a recognised level of competence and experience are chosen
to perform this type of test. This aspect in further reflected in this module.
Role of PT in the accreditation process
One of the most applications of PT schemes is the use in the accreditation process
of testing or calibrating laboratories [7,8,9]. Furthermore, EN 45001 "General requirements
for the competence of testing and calibration laboratories" [10] and ISO- Guide
25-1990 [11], recommend that accredited laboratories and applicant laboratories
participate in proficiency testing or other interlaboratory comparisons as required
by the accreditation body or regulating authority. The European standard EN 45002,
"General criteria for the assessment of testing laboratories" [12], demands related
to proficiency testing:
- " An accreditation body may, where judged appropriate, require testing laboratories
to participate in proficiency testing.
- " If the results of the participation in the required proficiency testing are unsatisfactory,
the granting or maintenance of accreditation shall be reconsidered.
- " However, an accreditation shall not be granted or maintained only on the basis
of the results of proficiency testing.
- " These proficiency testing schemes may be organised by the accreditation body itself
or by any other body judged competent.
- " Proficiency testing should be consistent with the provisions contained in ISO/IEC
Guide 43, "Proficiency Testing by interlaboratory comparison".
- As we see, proficiency testing and the accreditation process are closely connected.
Therefore the accreditation bodies have to have policies on how they want to use
proficiency testing in the accreditation process [13]. In Germany, there are no
requirements for a participation in PT schemes for laboratories working in the non-
regulated area, but the participation in, e.g. environmental and/or chemical measurements
is strongly recommended and controlled during surveillance visits for the most important
testing fields.
- In the mandatory area, the requirements on participation are based on decrees of
the Länder authorities.
Purpose of proficiency testing - (Why participate?)
Bodies assessing the technical competence of testing laboratories normally require
or expect satisfactory participation in proficiency testing as evidence of a laboratory's
ability to produce reliable test results, except where proficiency testing is inappropriate.
However, it is emphasised that a major distinction exists between:
- The evaluation of the competence of a laboratory by the assessment of its total
operation against pre- determined requirements, and
- The examination of the results of a laboratory's participation in proficiency testing
which may only be considered as given information about the technical competence
of the testing laboratory at a single point of time under the specific conditions
of the test for tests involved in a particular proficiency testing scheme.
The need of proficiency testing schemes
PT schemes are especially necessary, when the assessor is not able to give a positive
judgement on the performance of a testing laboratory based only on the on- site
assessment. In his judgement internal and external quality management activities
must be implemented. He has to take into account the following essential points,
which should be fulfilled by the laboratory prior to accreditation.
- Internal or external comparison tests performed by the laboratory.
- Are calibrations performed on a regular base?
- Does the laboratory use certified reference materials or own standards regularly?
- Does the laboratory use duplicate or repeated measurements?
- Does the laboratory use blind test items?
Additionally, PT schemes are necessary when:
- The competence of the staff might not be sufficient for the specific test!
-
Technical assessor decides that the experiences of the laboratory does not meet
the requirements of new test methods, new matrices, and new materials!
- The documentation
of in-house procedures seemed to be not sufficient!
- Results of PT schemes in other related fields of testing have not been fully satisfactory.
- The documentation of corrective actions after achieving unsatisfactory performance
is insufficient!
- Systematic errors are detected in the laboratory!
If these essential aspects are not completely fulfilled, the assessor should demand
a PT scheme, if necessary he should prepare a bilateral PT. In any case he has to
take the outcome of PT schemes organised under the supervision of the accreditation
body into account when he is judging about the competence of a testing/ calibration
laboratory (see part 2.9). Several other documents like the WECC document 15-1992
[14] or APLAC documents on Interlaboratory Comparisons [15,16] and others [17-20]
describe the use of proficiency testing.