Abundance ratios versus velocity dispersion, σ, for SDSS stacked spectra of ETGs (see the text for details). Each panel corresponds to a different element, as labeled. Thin and thick lines show results obtained by fitting 1SSP and 2SSP models, respectively. Dotted, dashed, and solid lines denote different fitting techniques. Different models are shown in different colors, i.e., blue for E-MILES BaSTI, red for E-MILES Padova00, and green for CvD18. Gray dots show the [X/Fe] versus σ trend from Conroy et al. (2014), based on a different set of SDSS stacked spectra.