Contribution of principal components. Top panel: scree plot using the PCA and showing the contribution (as a percentage) of the five principal components (PCs) to the overall variance in the dataset. Bottom panels: contributions of the original variables: the AGN luminosity at 5100 Å (L_5100 Å, in units of erg s⁻¹); the FWHM of the polarized and unpolarized Hα emission line (in units of km s⁻¹); and the EW for the corresponding Hβ and optical Fe II emission within 4434−4684 Å (in units of Å) to the first two PCs. The red dashed line indicates the expected average contribution.