Accreditation and Quality Assurance

, Volume 13, Issue 4–5, pp 231–238 | Cite as

Performance of uncertainty evaluation strategies in a food proficiency scheme

General Paper


A study of the performance of different uncertainty evaluation strategies among 163 voluntary respondents from food proficiency schemes is presented. Strategies included use of: single-laboratory validation data, quality control data, past proficiency testing data, reproducibility data, a measurement equation and the dispersion of replicate observations on the test material. Most performed reasonably well, but the dispersion of replicate observations underestimated uncertainty by a factor of approximately 3. Intended compliance with accreditation requirements was associated with significantly improved uncertainty evaluation performance, while intended compliance with the ISO “Guide to the expression of uncertainty in measurement” had no significant effect. Substituting estimates based on the Horwitz or Horwitz–Thompson models or on PT target standard deviation for the respondents’ own estimates of uncertainty led to a marked reduction in poor zeta scores and significant improvement in dispersion of zeta scores.


Uncertainty evaluation Proficiency testing Reproducibility 



This study was supported under contract with the Department of Innovation, Universities and Skills as part of the Valid Analytical Measurement programme.


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Copyright information

© LGC Limited 2008

Authors and Affiliations

  1. 1.LGC LimitedMiddlesexUK
  2. 2.Central Science LaboratoryYorkUK

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