Incidences from the literature for both GRB and quasar absorbers. Symbols are colour coded with all quasar samples shown in blue and GRB samples in black. Incidences from the low-spectral-resolution GRB sample from Fynbo et al. (2009) were re-analysed in this work. This low-resolution data set is also part of the sample compiled by Cucchiara et al. (2013). The dashed and dotted curves show expectations from SDSS quasar data from Prochter et al. (2006a) and Zhu & Ménard (2013), respectively, and the solid line the incidence towards quasars measured with high-spectral-resolution data (Mathes et al. 2017).