Just because a valid
method exists, does not
mean that sampling can
be ignored.

 

Robustness is the ability to remain unaffected by small variations in the method parameters. This is measured by the ability to remain unaffected by small but deliberate variations in method parameters and provides an indication of its reliability during normal usage. In essence, robustness measures intra-laboratory variation.

Ruggedness is the reproducibility of results obtained under varying conditions such as different laboratories and different equipment. In essence, ruggedness measures inter-laboratory variation. Different laboratories performing a ring test measure ruggedness. Ruggedness is the last criterion to be measured, if a method has not satisfied the previous criteria then a ring test should not be performed.

Just because a valid method exists, does not mean that sampling can be ignored. Correct sampling is just as important as correct testing methodology. The following three statistical definitions are of great importance when discussing sampling.

• Population is the set of all measurements of interest. If we wanted to know the per cent Bt in a one hundred seed sample, we could assay each seed and determine the true percent Bt in the population.

• Sample is the subset of measurements selected from a population. An example would be to test one hundred seeds out of a population of two thousand.

• Statistical Inference is a conclusion about a population based on information contained in a sample(s).

 

Without a representative sample or a sample that is too small, the confidence in a statistical inference is very low. There are two common sampling methods that are applicable to seed testing. One is sequential sampling, which allows one to maintain the power of a larger sample size even though a smaller sample is tested. A second method is Bayesian methods that allow for the combination of different testing results. An example would be the combination of field results and laboratory results. Richard Vierling

 

Editor’s Note: Dr. Richard Vierling is the Genetics Lab Director for the Indiana Crop Improvement Association and also works with the Department of Agronomy at Purdue University.

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