Mean slope for the f_X − f_UV relation for the case of Γ = 1.7−2.8, evaluated as the arithmetic mean of all the slopes in the redshift bins with more than five objects, as a function of k δ_obs, that is of the amount of sources excluded from the sample because of the selection for the Eddington bias (see text for details). The mean slope is flatter for low values of k, reaches a maximum of γ ∼ 0.58 and then drops back while k increases. Mean dispersion as a function of k δ_obs is listed in blue, while in black the number of sources surviving the selection for each k δ_obs choice.