smaller value of $r_0$ is expected for their sample, because the clustering strength is found to depend, weakly, on the absolute magnitude $M_B$, as shown in @ximb and in @2dfgal.

@gs94 investigated the clustering properties of 192 Seyfert galaxies from the IRAS All Sky Survey. They claimed a $2-3\sigma$ detection at $10-20 h^{-1}$ Mpc, corresponding to $\bar{\xi}(20)=0.14\pm0.15$ at $\bar{z}=0.05$, similar to local late-type galaxies. This result is consistent with a model in which local QSOs randomly sample the galaxy distribution.

@carrera analyzed the clustering of 235 X-ray selected AGN with $0\le z\le 3$, obtaining an integrated TPCF of $0.02\le \bar{\xi}(20) 
\le 0.25$. The redshift range of this survey is particularly extended and the density of sources correspondingly low. The clustering detection is marginal, at $2\sigma$ level only. Moreover there are only 33 AGN with $z\le 0.2$ in this sample.

@akylas investigated the angular correlation function of 2096 sources selected from the RASS-BSC. They rejected known stars and other contaminants: a cross-correlation analysis with spectroscopic samples indicated that the majority of their sources are indeed AGN. They obtained a $\sim 4\sigma$ detection of clustering. Using the Limber equation and assuming a source redshift distribution (not shown in their paper) with an 