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Jolliffe I. Principal Component Analysis (2ed., Springer, 2002)(518s)

Jolliffe I. Principal Component Analysis (2ed., Springer, 2002)(518s)

Jolliffe I. Principal Component Analysis (2ed., Springer, 2002)(518s)

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5.1. Plotting Two or Three <strong>Principal</strong> <strong>Component</strong>s 83Figure 5.1. (b). Student anatomical measurements: plot of the first two PCs for28 students with minimum spanning tree superimposed.Artistic Qualities of PaintersThe second data set described in this section was analysed by Davenportand Studdert-Kennedy (1972). It consists of a set of subjective measurementsof the artistic qualities ‘composition,’ ‘drawing,’ ‘colour’ and‘expression’ for 54 painters. The measurements, on a scale from 0 to 20,were compiled in France in 1708 by Roger de Piles for painters ‘of establishedreputation.’ Davenport and Studdert-Kennedy (1972) give data for56 painters, but for two painters one measurement is missing, so thesepainters are omitted from the analysis.Table 5.1 gives the variances and coefficients for the first two PCs basedon the correlation matrix for the 54 painters with complete data. The components,and their contributions to the total variation, are very similar tothose found by Davenport and Studdert-Kennedy (1972) for the covariancematrix. This strong similarity between the PCs for correlation andcovariance matrices is relatively unusual (see Section 3.3) and is due to thenear-equality of the variances for the four variables. The first component

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