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en:pca [2019/02/25 19:08]
David Zelený [Ordination analysis]
en:pca [2019/02/27 14:57]
David Zelený [The circle of equilibrium contribution]
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-Section: Ordination analysis+Section: [[en:ordination]]
 ===== PCA & tb-PCA (linear unconstrained ordination) ===== ===== PCA & tb-PCA (linear unconstrained ordination) =====
    
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 ==== The circle of equilibrium contribution ==== ==== The circle of equilibrium contribution ====
-The circle sometimes projected onto ordination diagram to estimate the importance of individual species/descriptors/variables. The radius is calculated as √(//d/////p//), where //d// is the number of displayed PCA axes (usually //d// = 2) and //p// is the number of variables (columns in the dataset). The arrow of the same length as the circle radius contributes equally to all axes in PCA; arrows longer than circle radius make a higher contribution than average and can be interpreted with confidence (in the context of given number of ordination axes, here two, <imgref pca_circle_eq_contrib>).+The circle sometimes projected onto ordination diagram to estimate the importance of individual species/descriptors/variables. The radius is calculated as √(//d/////p//), where //d// is the number of displayed PCA axes (usually //d// = 2) and //p// is the number of variables (columns in the dataset). The descriptor with a vector of the same length as the circle radius contributes equally to all axes in PCA; vectors extending the circle radius make a higher contribution than average to the current display and can be interpreted with confidence (in the context of given number of ordination axes, here two, <imgref pca_circle_eq_contrib>).
  
 <imgcaption pca_circle_eq_contrib|Circle of equilibrium contribution projected onto PCA ordination diagram. PCA based on wetland water chemistry dataset.>{{obrazky:pca_circle_of_eq_contrib.jpg |}}</imgcaption> <imgcaption pca_circle_eq_contrib|Circle of equilibrium contribution projected onto PCA ordination diagram. PCA based on wetland water chemistry dataset.>{{obrazky:pca_circle_of_eq_contrib.jpg |}}</imgcaption>
  
  
en/pca.txt · Last modified: 2020/03/29 10:52 by David Zelený