Authors: Stephen L R Ellison
Publish Date: 2015/09/07
Volume: 20, Issue: 6, Pages: 519-528
Abstract
Homogeneity assessment of reference materials is discussed with particular reference to the recommendations given in ISO Guide 35 It is suggested that Guide 35 could be improved by the addition of a wider range of experimental designs and by using statistical power calculations to improve the recommendations for design of experiments for homogeneity assessment It is further shown that the present recommended allowance for possible inhomogeneity uncertainty in the absence of a significant betweenbottle effect does not have a sound statistical basis and is considerably smaller than an accurate upper 95 confidence limit for the betweenunit term Alternatives are considered including the use of a more accurate and usually much larger calculation of possible betweenunit variance post hoc power calculation and the simple use of the calculated betweenunit variance coupled with increased emphasis on effective experimentation to limit the risk of underestimation Recommendations for improved guidance are made
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