Random samples of each of several food products were obtained from defined lots during processing or
from retail outlets. The foods included raw milk (sampled on farm and from a bulk-milk tanker), sprouted
seeds, raw minced meat, frozen de-shelled raw prawns, neck-flaps from raw chicken carcasses and
ready-to-eat sandwiches. Duplicate sub-samples, generally of 100 g, were examined for aerobic colony
counts; some were examined also for counts of presumptive Enterobacteriaceae and campylobacters. After
log10-transformation, all sets of colony count data were evaluated for conformity with the normal
distribution (ND) and analysed by standard ANOVA and a robust ANOVA to determine the relative
contributions of the variance between and within samples to the overall variance. Sampling variance
accounted for >50% of the reproducibility variance for the majority of foods examined; in many cases it
exceeded 85%.We also used an iterative procedure of re-sampling without replacement to determine the
effects of sample size (i.e. the number of samples) on the precision of the estimate of variance for one of the
larger data sets. The variance of the repeatability and reproducibility variances depended on the number of
replicate samples tested (n) in a manner that was characteristic of the underlying distribution. The results
are discussed in relation to the use of measurement uncertainty in assessing compliance of results with
microbiological criteria for foods.