Figure 11: Fraction of obscured AGN (  cm−2) as a function of redshift for a sample of AGN selected at high energies from INTEGRAL observations, as shown by Malizia et al. [68]. All of these sources have X-ray luminosities lower than 1046 erg s−1. The remarkably strong decline in this fraction at is likely due to selection effects and not intrinsic to the AGN population. That the fraction of CT AGN in the first bin is ~20%, in contrast to the ~5% found overall suggests that current hard X-ray surveys are not sensitive enough to observe CT AGN beyond . This will improve dramatically with NuSTAR [69].