Evaluating participant performance in qualitative PT/EQA schemes

A basic principle that needs to be satisfied before a proficiency testing (PT)/external quality assessment (EQA) scheme is first introduced is that measurement and assessment of performance is possible. For qualitative analyses, data can be presented as ??percentage correct??, and these data can be aggregated to show trends and to facilitate monitoring performance over time. Alternatively data can be analysed to identify significant patterns or changes in practice, or to compare different categories. However, the most useful tool is the application of a numerical score to the results. A number of different scoring strategies can be used, varying in complexity depending on the nature and significance of the type of results generated. Examples from selected microbiological EQA schemes are presented.