Proficiency testing in analytical laboratories: how to make it work

Abstract This paper covers the role of proficiency testing schemes in providing an occasional but objective means of assessing and documenting the reliability of the data produced by a laboratory, and in encouraging the production of data that are "fit-for-purpose". A number of aspects of proficiency testing are examined in order to highlight features critical for their successful implementation. Aspects that are considered are: accreditation, the economics and scope of proficiency testing schemes, methods of scoring, assigned values, the target value of standard deviation σp, the homogeneity of the distributed material, proficiency testing in relation to other quality assurance measures and whether proficiency testing is effective. Stress is placed on the importance of any proficiency testing scheme adhering to a protocol that is recognised, preferably internationally. It is also important that the results from the scheme are transparent to both participating laboratory and its "customer".