Accreditation and Quality Assurance

, Volume 10, Issue 10, pp 521–526 | Cite as

Interpretation of interlaboratory comparison results to evaluate laboratory proficiency

  • Rob G. Visser
General Paper


Guidelines are given for the evaluation of proficiency test (PT) results in order to increase the effectivity of PT participation. For better understanding, some statistical background is given along with some examples to show the effects of the choices made by the PT provider. The calculation method of the assigned value and the selection of the standard deviation both affect the z-score that is used by the participating laboratory to judge the quality of its performance in the PT. Therefore, the participating laboratory is advised to use the PT results with care and, if necessary, to recalculate the z-scores. Finally, advice is given on how not to follow up bad PT results along with some valuable steps that could be part of an effective follow-up procedure.


Proficiency test Assigned value Standard deviation z-score Root cause analysis Corrective action Effectivity 


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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • Rob G. Visser
    • 1
  1. 1.Institute for Interlaboratory StudiesSpijkenisseThe Netherlands

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