Closure of analytical chemical data and multivariate classification.
When it is not possible to analyze an exactly reproducible amount of sample (or whenever samples contain indefinite amounts of extraneous materials) it is customary to normalize the data by making, for example, the sum of the concentrations obtained for each sample equal to 100. Although the data normalized (or ;closed') in such a manner have been criticized, it is empirically shown that closure is appropriate in order to compare and classify samples of the type indicated above.
Aruga
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Department of Analytical Chemistry, University of Turin, via Giuria 5, 10125 Turin, Italy.