Precision and accuracy of test methods and the concept of K-factors in chemical analysis

Abstract

Standard methods of analysis are being continuously developed by national (BSI) and international (ISO) committees to produce methods with the precision and accuracy to enable materials to be analysed to more demanding criteria. Following development, they undergo inter-laboratory tests to evaluate performance. An ISO Standard (ISO) 5725, “Precision of Test Methods—Determination of Repeatability and Reproducibility for a Standard Test Method by Inter-laboratory Tests,” has been prepared as a guide to such trials.

This paper introduces and explains the significance of terms defined in the Standard and discusses the objectives of inter-laboratory tests. It also interprets these by reference to the trials undertaken to test standard methods developed for the analysis of iron, steel and iron ores. In particular, the relationship between these data and the concept of K-factors suggested by Johnson and others to relate precision and accuracy with concentration is discussed. The significance of K-factors in day-to-day laboratory operation is also considered.