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It is very important to realize that the well-known 'zeros problem' in compositional data is inherent in the nature of the data rather than in the log-ratio methodology. In a strict sense, any null value is informative itself and needs specific treatment before a multivariate method is applied. In the rounded zero case specific techniques of missing data should be applied as a previous step, taking into account that any of these techniques must respect the compositional nature of the data. In practice, when an imputation method is applied, then it is necessary to make a sensitivity analysis of the results from multivariate analysis. These methodological aspects are applied and illustrated using compositional data from geological samples.

Suitable statistical methods for compositional data based on log-ratio methodology are not included in standard statistical packages. This work presents a detailed guide to freeware Excel for Windows-based package, named CoDaPack, which implements most of the basic statistical methods of this methodology. The web site http://ima.udg.es/~thio/#Compositional Data Package contains this freeware package and to install it users need only to have Excel installed on their computers. The guide starts with an example in order to show how to work with this software and ends with a description of all features of CoDaPack.a part of Inputs structure, this part must be marked inside Inputs structure and the arrow which now indicates the opposite direction should be pressed.