Performing Common Analyses and Obtaining Statistics

Chapter 7 Performing Common Analyses and Obtaining Statistics 249... 

Sc (Figure 4.5.5) shows a suprising distribution of effects. Whereas the sampling variance is around 100%, the variance obtained for the different factors tested is even larger. As the concentration of this element is very low, it is impossible to identify any trend in the distribution variance. All of the elements studied have in common a lack of influence of the blanks on the results whereas the influence of the other effects tested varies from one element to another. Further statistical analyses were performed using STAGRAPHICS software, for the three elements (B, Sc and Zn) identified on the basis of the raw data without subtracting the analytical uncertainty. The results obtained are described below. 

As described in Section 3.2, interlaboratory studies are organized in such a way that several laboratories analyse a common material which is distributed by a central laboratory responsible for the data collection and evaluation. When laboratories participate in an interlaboratory study, different sample pretreatment methods and techniques of separation and final determination are compared and discussed, as well as the performance of these laboratories. If the results of such an intercomparison are in good and statistical agreement, the collaboratively obtained value is likely to be the best approximation of the truth. 

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