Technical rule 2012-02
DIN ISO/TR 22971 (DIN SPEC 55318) provides users with practical guidance to the use of ISO 5725-2:1994 and presents simplified step-by-step procedures for the planning, implementation, and statistical analysis of inter-laboratory studies for determining the variability of a standard measurement method and on the determination of repeatability and reproducibility of measuring values obtained in inter-laboratory testing. ISO 5725 consists of six parts. ISO 5725-2 was developed as a guidance document for ISO Technical Committees and other organizations responsible for undertaking inter-laboratory studies for characterizing the variability of standard measurement methods. Two measures of variability, repeatability and reproducibility, are accepted in many disciplines as representative of data encountered in measurement processes. Repeatability refers to the variability among measurements made on nominally identical samples or materials under identical circumstances. It is recognized that, because of unknown or uncontrollable factors which influence the measurement process, repeated measurements will usually not agree. The extent of this variability can be expressed by a standard deviation, called the repeatability standard deviation, of the results of within-laboratory comparisons. Reproducibility refers to the variability among measurements made on identical samples or materials under differing conditions by different laboratories following the same standard measurement method. Reproducibility includes effects caused by differences among instruments, reagents, operators, laboratories, and environmental conditions. The variability of results under these conditions may be described by a standard deviation called the reproducibility standard deviation. This guidance document is divided into four clauses in addition to the Scope (clause 1): - Clause 2, Organization of an inter-laboratory programme, deals with the organization of the inter-laboratory test and covers the roles of the executive officer, laboratory personnel, and statistician in preparing for and administering the test, the choice of materials and levels of interest for the test, and the selection of laboratories. It also describes how the number of replicate measurements (to be made on each sample) is to be statistically treated and the manner in which the resulting data are to be reported. - Clause 3, Critical examination of the data, deals with measuring results using graphical and numerical methods. Guidance is given as to when data are anomalous, that is, if they are inconsistent with other measuring values from the study, and for outlier tests that are used to identify the presence or absence of anomalous measuring values. - Clause 4, Estimation of repeatability and reproducibility standard deviations, deals with the estimation and interpretation of repeatability and reproducibility standard deviations. Also included is a comparison of the relative contributions of the repeatability and reproducibility standard deviations to the total variability of the test method. - Clause 5, Worked examples using statistical software, deals with worked examples that highlight various techniques that can be used. It is recommended that this guidance document be read in conjunction with ISO 5725-2 and should not be used as a replacement for ISO 5725-2.