Rest equivalent width of the C IVλ1549 Å emission line, as obtained from our custom fits of the SDSS spectra, plotted against Δα_ox. There is a hint of a possible correlation, confirmed at the 98.5% significance by the Pearson’s ρ and Kendall’s τ tests. For reference, we also show the typical thresholds for two quasar populations known to exhibit enhanced rates of X-ray weakness, that is, BAL (Δα_ox <  −0.3; Liu et al. 2018) and weak-line (extreme subset: C IV REW < 7 Å; bridge subset: C IV REW = 7−15.5 Å; Ni et al. 2018) quasars.