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  • 578.77  (1)
  • Graphics  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of classification 13 (1996), S. 81-105 
    ISSN: 1432-1343
    Keywords: Dimensionality reduction ; Distances ; Graphics ; Multidimensional scaling ; Symmetric matrices ; Unfolding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Graphical displays which show inter-sample distances are important for the interpretation and presentation of multivariate data. Except when the displays are two-dimensional, however, they are often difficult to visualize as a whole. A device, based on multidimensional unfolding, is described for presenting some intrinsically high-dimensional displays in fewer, usually two, dimensions. This goal is achieved by representing each sample by a pair of points, sayR i andr i, so that a theoretical distance between thei-th andj-th samples is represented twice, once by the distance betweenR i andr j and once by the distance betweenR j andr i. Selfdistances betweenR i andr i need not be zero. The mathematical conditions for unfolding to exhibit symmetry are established. Algorithms for finding approximate fits, not constrained to be symmetric, are discussed and some examples are given.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2021-09-27
    Description: Fatty acid (FA) compositions provide insights about storage and feeding modes of marine organisms, characterizing trophic relationships in the marine food web. Such compositional data, which are normalized to sum to 1, have values—and thus derived statistics as well—that depend on the particular mix of components that constitute the composition. In FA studies, if the set of FAs under investigation is different in two separate studies, all the summary statistics and relationships between the FAs that are common to the two studies are artificially changed due to the normalization, and thus incomparable. Ratios of FAs, however, are invariant to the particular choice of FAs under consideration—they are said to be subcompositionally coherent. Here, we document the collaboration between a biochemist (M.G.) and a statistician (M.J.G.) to determine a suitable small set of FA ratios that effectively replaces the original data set for the purposes of univariate and multivariate analysis. This strategy is applied to two FA data sets, on copepods and amphipods, respectively, and is widely applicable in other contexts. The selection of ratios is performed in such a way as to satisfy substantive requirements in the context of the respective data set, namely to explain phenomena of interest relevant to the particular species, as well as the statistical requirement to explain as much variance in the FA data set as possible. Benefits of this new approach are (1) univariate statistics that can be validly compared between different studies, and (2) a simplified multivariate analysis of the reduced set of ratios, giving practically the same results as the analysis of the full FA data set.
    Keywords: 578.77
    Language: English
    Type: map
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