ISO TR 21074:2016 pdf free
ISO TR 21074:2016 pdf free.Application of ISO 5725 for the determination of repeatability
The structure of the precision test normally used within standardization work using chemical analysis is a 3-factor, staggered-nested structure, as shown in Figure 1.
a) Both A and B (Day 1) are obtained under repeatability where independent test results are obtained with the same method on identical items in the same laboratory by the same operator using the same equipment within short intervals of time.
b) C (Day 2) is obtained under time- different intermediate precision conditions, except for the time factor. The measurement is performed by the same operator and, in addition, the measurements at a given level are performed using the same sample and equipment throughout.
For a precision test it is important to use homogeneous samples. Therefore, it is necessary to control the homogeneity of the samples selected for each precision test, if the samples are not certified reference materials, before starting a test in order to be sure that the heterogeneity level of the sample can be included in the expected precision values.
In principle, the number of laboratories that participate in an international cooperative test is decided on the basis of the required precision. As this approach is often difficult to implement, the practical rule typically followed is the selection of 8 to 15 (or more) laboratories see ISO 5725-1:1994, 6.3.4, preferably in 5 countries. The number of levels depends on the range and scope of the method to be tested. A minimum of two levels by decade with the scheme (for example, 1-10) is required, and in the case of limited application ranges, three or more levels by decade (for example, 1-2-5-10) can be selected.
NOTE Fully-nested experiments offer higher reliability of repeatability than staggered-nested experiments.
However, it will not improve the reliability of reproducibility significantly. From the standpoint of improving reliability, it is effective to increase the number of participating laboratories.ISO TR 21074 pdf download.
