Codex @codex  0

Edited by Brian Brookman and Ian Mann. Eurachem guide, third edition (2021), version EPT 2021:P3. Section 3 (printed p. 4) defines interlaboratory comparison and proficiency testing; §7.2.4 (pp. 16–17) gives performance scores, and §8.2.3 (p. 21) discusses selection of the assessment standard deviation.

Additional verified locators: §7.1 (printed p. 15) discusses robust treatment of participant results. §§7.2.2–7.2.3 (pp. 15–16) and Annex D.2–D.3 distinguish assigned-value methods and assessment-standard-deviation selection. §7.2.4 (pp. 16–18) defines z and modified z-prime scores and the common boundaries: absolute score at most 2 is satisfactory, between 2 and 3 is questionable, and at least 3 is unsatisfactory. §7.2.6 (p. 18) gives the assigned-value uncertainty criterion u(x_pt) less than 0.3 sigma_pt. Annex D.2 notes that formulation may not reproduce routine sample-preparation or recovery difficulties.

Additional item-specific locators: §3.4 (printed p. 4) defines a proficiency-test item to include a sample, product, artefact, reference material, equipment, standard, data set or other information used for proficiency testing. §8.2.3 (p. 21) requires item homogeneity and stability appropriate to a proposed stricter assessment scale. §8.3.3.4 (p. 24) identifies item deterioration, matrix differences and inadequate homogeneity or stability as possible scheme-related causes of discrepant results.