IS0 5725-5: 1998 pdf download – Accuracy (trueness and precision) of measurement methods and results – Part 5: Alternative methods for the determination of the precision of a standard measurement method.
4 Split-level design 4.1 Applications of the split-level design 4.1.1 The uniform level design described in IS0 5725-2 requires two or more identical samples of a material to be tested in each participating laboratory and at each level of the experiment. With this design there is a risk that an operator may allow the result of a measurement on one sample to influence the result of a subsequent measurement on another sample of the same material. If this happens, the results of the precision experiment will be distorted: estimates of the repeatability standard deviation o, will be decreased and estimates of the between- laboratory standard deviation cq will be increased. In the split-level design, each participating laboratory is provided with a sample of each of two similar materials, at each level of the experiment, and the operators are told that the samples are not identical, but they are not told by how much the materials differ. The split-level design thus provides a method of determining the repeatability and reproducibility standard deviations of a standard measurement method in a way that reduces the risk that a test result obtained on one sample will influence a test result on another sample in the experiment. 4.1.2 The data obtained at a level of a split-level experiment may be used to draw a graph in which the data for one material are plotted against the data for the other, similar, material. An example is given in figure 1. Such graphs can help identify those laboratories that have the largest biases relative to the other laboratories. This is useful when it is possible to investigate the causes of the largest laboratory biases with the aim of taking corrective action. 4.1.3 It is common for the repeatability and reproducibility standard deviations of a measurement method to depend on the level of the material.