One way to improve laboratory performance is the participation in colaborative ring trials. It is recommended, that the organizer sends out more than one sample with differing analyte concentrations. The participating labs then measure the concentration of a number of analytes. Once the data is available to the organizer, he or she can then create correlation plots (Youden plots) of the concetration of 1 sample on the X and concentrations of another sample on the Y axis. This can be done with software packages like PROLab Smart which are specialised for such data. While such a correlation chart is quickly done in Excel, it get's very cumbersome if the number of analytes and samples is a bit larger - hence the need for specialised software. Another challange is to give the viewer an intuitive feeling whether results are ordinary or need attention.
Enter ISO 13528. In this standard, the use of ellipses is recommended for that purpose, advise I'll certainly follow in my next report.