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________________________________________________
Selection, use and interpretation
of proficiency testing (PT) schemes
by laboratories - 2000
________________________________________________
This document has been produced by the Eurachem Nederland, task group "Proficiency testing
schemes" (part of the working group on "Interlaboratory Studies"), and the
Laboratory of the Government Chemist (LGC), United Kingdom.
Production of this Guide was in part supported under contract with the UK Department of Trade and
Industry as part of the National Measurement System Valid Analytical Measurement (VAM)
Programme.
Comments are invited on this document and should be sent to the editor:
Mr Nick Boley
Convenor, EURACHEM Proficiency Testing Mirror Group
LGC, Queens Road, Teddington, Middlesex, TW11 0LY, United Kingdom
(
Int +44 20 8943 7311,
4
: Int +44 20 8943 0654,
:+
:
npb@lgc.co.uk
English Edition 1.0, 2000
Ruling language
The text may be freely translated into other languages, but where such action results in a dispute
over interpretation, the guidance given in this English version is taken as being the definitive version.
Copyright of text
Copyright of the guidance presented in this guide is the property of the organisations represented by
the authors as listed overleaf. Enquiries regarding the translation, and production and distribution of
new editions of this guide should be directed to the EURACHEM Secretariat.
 EURACHEM GUIDE ON SELECTION, USE AND INTERPRETATION OF PT SCHEMES
Edition 1.0 - 2000
Contents
Contents
i
Authors
ii
Summary
1
Samenvatting
1
1. Introduction and scope
3
1.1 Background and motivation to this document
3
2. Background and introduction to proficiency testing
5
2.1 Quality management system
5
2.2 Proficiency testing (PT) schemes: an introduction
6
3. Selection of PT schemes
9
3.1 How to find out if a specific proficiency testing scheme is organised?
9
3.2 How to decide if a proficiency testing scheme is relevant?
11
4. Interpretation of PT reports
12
4.1 Statistics
12
4.2 Split Level
17
4.3 z scores
18
5. Laboratory actions
21
5.1 Evaluation
21
5.2 Corrective Actions
27
5.3 Tasks and Functions
28
6. Conclusions
32
Appendices
Appendix 1: Judgement of relevancy of proficiency test 34
Appendix 2: Two examples of typical Youden plots 35
Appendix 3: Checklist for analysing the internal quality control data 37
Appendix 4: Interpretation of data for end-users of data of analytical laboratories
40
Appendix 5: About the authors of this guide
44
References
46
i
EURACHEM GUIDE ON SELECTION, USE AND INTERPRETATION OF PT SCHEMES
Edition 1.0 - 2000
Authors
Eurachem Nederland, task group "Proficiency testing schemes"
(part of the working group on "Interlaboratory Studies")
•
Mr. G. Counotte: Gezondheidszorg voor Dieren, Deventer
•
Mrs. D. Van Dijk: Wageningen Agricultural University, Wageningen
•
Mrs. D.C. Van Loenen-Imming: KEMA, Arnhem
•
Mr. W. Oussoren: Institute for Interlaboratory Studies, Dordrecht
•
Mrs. B. Van der Vat: TNO Nutrition and Food Research Institute, Zeist
•
Mr. R.G. Visser: Institute for Interlaboratory Studies, Dordrecht
Laboratory of the Government Chemist (LGC), Middlesex, United Kingdom
•
Mr. N. Boley
•
Mr. J. Day
Dr. R. Walker
ii
EURACHEM GUIDE ON SELECTION, USE AND INTERPRETATION OF PT SCHEMES
Edition 1.0 - 2000
Summary
This document represents the current (2000) state-of-the-art with respect to the selection
and use of proficiency testing schemes, and the interpretation of results and evaluations
given in proficiency testing schemes. Although this is aimed primarily at staff in analytical
laboratories, it is also useful for customers of laboratories, assessors working for
accreditation bodies and other external users of PT scheme results.
The correct use and interpretation of PT scheme results is complex. This guide is
designed to enable users of these results to gain a better understanding of proficiency
testing, and therefore how to use the results it produces in a more sophisticated and
appropriate manner. It gives guidance to laboratory staff at all levels on how to place
results in context, and how to use the results to gain an overall picture of the quality of
performance.
Proficiency testing is a quality assurance tool which is evolving very quickly. Therefore
this document should be viewed as a “living document” which will be subject to
continuous revision over the next few years. As developments occur, the document will
be revised, and updated versions made available subsequently.
Samenvatting
Dit document beschrijft de huidige (2000) 'state-of-the-art' situatie met betrekking tot de
keuze en het gebruik van 'Proficiency Testing' (PT) schema's en de interpretatie van de
resultaten en evaluaties gegeven in proficiency testing schema's. Hoewel het document
zich met name richt op het management in analytische laboratoria is het ook bruikbaar
voor klanten van laboratoria, assessoren die werkzaam zijn bij accrediterende instanties
en andere externe gebruikers van PT schema resultaten.
Het correcte gebruik en de interpretatie van PT schema resultaten is complex. Deze
handleiding is geschreven om gebruikers van de resultaten een beter inzicht te geven in
proficiency testing. Dit om zo het juiste gebruik van de PT resultaten te bevorderen. De
1
EURACHEM GUIDE ON SELECTION, USE AND INTERPRETATION OF PT SCHEMES
Edition 1.0 - 2000
handleiding geeft een handreiking aan het het gehele laboratoriummanagement over hoe
de resultaten in de juiste context geplaatst moeten worden en hoe resultaten gebruikt
kunnen worden om een totaalbeeld van het presteren van het laboratorium te verkrijgen.
Proficiency testing schema's vormen één van die gereedschappen van kwaliteitsborging
('quality control', QC) die zich zeer snel ontwikkelen. Dit document moet daarom gezien
worden als een levend document waarvan de komende jaren regelmatig een revisie zal
verschijnen. Zodra zich nieuwe ontwikkelingen voordoen zal het document worden
bijgewerkt en de ge-update versies zullen daarna beschikbaar worden gemaakt.
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