Analysing collaborative trials for qualitative microbiological methods: accordance and concordance.

In qualitative (detection) food microbiology, the usual measures of repeatability and reproducibility are inapplicable. For such studies, we introduce two new measures: accordance for within laboratory agreement and concordance for between laboratory agreement, and discuss their properties. These measures are based on the probability of finding the same test results for identical test materials within and between laboratories, respectively. The concordance odds ratio is introduced to present their relationship. A method to test whether accordance differs from concordance is discussed.