PCA horseshoe effect

[topepo]

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The PCA plot of the barley data shows a pattern reminiscent of the horseshoe effect. We should mention this. See

• PCA ordination notes
• What is the "horseshoe effect" and/or the "arch effect" in PCA / correspondence analysis?
• Noise Reduction By Eigenvector Ordinations
• Detecting the Guttman effect with the help of ordinal correspondence analysis in synchrotron X-ray diffraction data analysis
• Horseshoes in multidimensional scaling and local kernel methods