Performance of uncertainty evaluation strategies in a food proficiency scheme |
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Authors: | Stephen L R Ellison Kenneth Mathieson |
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Institution: | (1) LGC Limited, Queens Road, Teddington, Middlesex, TW11 0LY, UK;(2) Central Science Laboratory, Sand Hutton, York, YO41 1LZ, UK |
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Abstract: | 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. |
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Keywords: | Uncertainty evaluation Proficiency testing Reproducibility |
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