Scoring the sum of correlated results in analytical proficiency testing

Abstract

In proficiency tests the participants' results are usually converted into scores. In some schemes the participants are required to report the sum of the concentrations of a number of analytes and this total also is converted into a score. In such instances the scoring procedure for the total should be mathematically consistent with that for the separate analytes. When these analytes are determined from a single test portion, however, the errors in the results from a participant are likely to be correlated because some stages of the analysis are common to all of the analytes. For a consistent outcome, the scoring method must take account of such correlation.