Radio loudness vs. redshift of XQSOs from COSMOS (circles) and XXL-S (diamonds). In different panels radio loudness is defined as: (a) 1.4 GHz radio luminosity, (b) IR-to-1.4 GHz luminosity ratio, q_TOT, (c) 1.4 GHz radio-to-optical luminosity ratio, (d) 1.4 GHz radio-to-X-ray luminosity ratio. Different thresholds from the literature, used to select sources as RL, are shown as indicated in the legends. The gray dot-dashed line and area show the q_TIR(z)±0.35 by Delhaize et al. (2017).