Estimation of sampling uncertainty of pesticide residues based on supervised residue trial data

Typical sampling uncertainties were calculated as the average of relative standard deviations (CV) of residues measured in individual crops tested in supervised residue trials and from their pooled variance for crop groups. The relative confidence intervals of the sampling uncertainty for different crops were estimated from the random duplicate composite samples generated with computer modeling from residues in 182 independent primary sample sets, each consisting of 100-320 residue data. The relative 95% confidence intervals were found to be independent from the CV of primary residue data populations; therefore, the calculated values are generally applicable. In view of the potentially serious consequences of underestimated sampling uncertainties, their upper confidence limits are recommended for practical use to verify the compliance of products and for planning statistically based sampling programs. Sampling uncertainties are reported for 24 crop groups and 106 individual crops.