Chapter 10 - Measurement uncertainty in microbiological analysis

Abstract

Measurement uncertainty is a metrological concept required to demonstrate trueness (accuracy) and precision of analytical work undertaken in laboratories. Two approaches are possible: the ‘bottom-up’ method requires identification of repeatability (r) and reproducibility (R) for all stages in an analytical procedure followed by their combination to provide an overall estimate. It is now widely accepted that such an approach is unsuitable for most microbiological estimations, not least because the target analytes are viable microbes numbers of which may fluctuate and are not constant. The alternative approach is the ‘top-down’ approach for which estimates of r and R are determined by inter- or intra-laboratory experiments. The chapter describes the background to and definitions of uncertainty and considers not only quantitative estimates, such as colony counts, but also results from quantal methods. The importance of sampling uncertainty is also discussed. Practical assessment of uncertainty is covered in the next chapter.