Assessment of the measurement method precision in interlaboratory test by using the robust “Algorithm S”

Abstract

The application of robust statistical methods to assess the precision (uncertainty) of the results of interlaboratory testing of measurement method is presented. These results may include outliers. An usual rejection of such data reduces the reliability of evaluation, especially for small samples. And the robust methods take into consideration all the sample data (also with outliers). The use of two robust methods are provided for international rules of comparative studies in accredited laboratories. However, there is a lack of instructions on how to proceed them in practice. Evaluation of the precision of results, using the same method for homogeneous objects in nine laboratories, was presented. By traditional calculations, the estimate of the standard deviation was 1.5 times higher without rejection of outlier in comparison to one with rejection of outlier. Then, after using the robust method “Algorithm S”, the obtained value was near the lower of two mentioned above, and with greater reliability.