Rest-frame monochromatic luminosities log L_X against log L_UV for the final “best” sample of 545 quasars (orange circles) as described in Sect. 2. The results from the emcee regression (black solid line) are also reported. Red thin lines represent 100 different realisations of the L_UV−L_X relation. The lower panel shows the residuals of log L_X and log L_UV with respect to the emcee best-fit line.