title: The interlaboratory performance of microbiological methods for food analysis.
abstract: Repeatability and reproducibility data for microbiological methods in food analysis were collated and assessed with a view to identifying useful or important trends. Generalized additive modeling for location, shape, and scale was used to model the distribution of variances. It was found that mean reproducibility for log10(CFU) data is largely independent of concentration, while repeatability SD of log10(CFU) data shows a strongly significant decrease in repeatability SD with increasing enumeration. The model for reproducibility SD gave a mean of 0.44, with an upper 95th percentile of approximately 0.76. Repeatability variance could be described reasonably well by a simple dichotomous model; at enumerations below 10(5)/g, the model for repeatability SD gave a mean of approximately 0.35 and upper 95th percentile of 0.63. Above 10(5)/g, the model gave a mean of 0.2 and upper 95th percentile of 0.36. A Horwitz-like function showed no appreciable advantage in describing the data set and gave apparently worse fit. The relationship between repeatability and reproducibility of log10(CFU) is not constant across the concentration range studied. Both repeatability and reproducibility were found to depend on matrix class and organism.
authors.affiliation: LGC Ltd, Queens Rd, Teddington, Middlesex, TW11 0LY, United Kingdom. s.ellison@lgc.co.uk
authors.forename: Stephen L R
authors.initials: SL
authors.lastname: Ellison
authors.forename: Pauline
authors.initials: P
authors.lastname: Key
authors.forename: Roger
authors.initials: R
authors.lastname: Wood
mesh_terms: D000821:Animal Feed / Q000382:microbiology; D001431:Bacteriological Techniques / Q000592:standards*; D005516:Food Microbiology / Q000379:methods* / Q000592:standards*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity