Best-fitting intrinsic absorption function in the redshift range 3 ≤ z ≤ 6 for the PDE model (dotted line). The boxes show the credible regions that correspond to 1σ confidence intervals of the posterior probabilities. The points represent the best-fitting results when using the LDDE model along with the 1σ uncertainties. For reference, shown are the results of Vito et al. (2018) re-scaled to the bins of our analysis (dashed line). The solid line presents their original absorption function; it is normalised between log N_H = 20 − 25.