Handling False Negatives, False Positives and Reporting Limits in Analytical Proficiency Tests

Abstract

The Harmonised Protocol on proficiency testing produced by ISO, IUPAC and AOAC International recommends that participants’ results on interval or ratio scales are converted to z-scores for assessment. When proficiency tests are conducted with materials that contain little or no analyte (simulating real conditions in residue analysis) scheme organisers have reported difficulty with applying the z-scoring system when false negatives and false positives occur. This paper concludes that the z-scoring system is adaptable without change to false negatives and positives, although a degree of statistical expertise is called for.