Ross et al. (2012; and references therein) has full details.

However, a uniform selection was performed on a subsample of the DR9 quasar targets. This uniform sample was selected by the “Extreme Deconvolution" (XD; Bovy, Hogg & Roweis 2009) algorithm which is applied to model the distribution in flux and flux uncertainty of a training set of quasars and stars (XDQSO; Bovy et al. 2011). The DR9Q has a flag which indicates if a quasar was selected in this uniform manner. In this paper we select all quasars in the DR9Q catalog with “uniform $>0$" which represent a statistical sample for clustering studies (P[â]{}ris et al. 2012; White et al. 2012). Additionally, we limit the SDSS DR9 quasar sample to be in the redshift range $2.2<z<3.5$. The median redshift of the final selected SDSS DR9 quasar sample is $z=2.5$.

![image](dr7dr9qso_Nz.eps){height="2.6in" width="3.45in"} ![image](dr7dr9_z_vs_MI.eps){height="2.6in" width="3.45in"}

### Stripe 82

Stripe 82 is an equatorial region that the Sloan Digital Sky Survey (SDSS) has repeatedly imaged up to 80 times (Abazajian et al. 2009) giving coadded optical data $\sim$2 magnitudes deeper than the single epoch SDSS observations. The Stripe 82 field covers approximately a 270 deg.$^2$ area ($-50^{\circ} < $RA$ < 59^{\circ}$, $-1.25^{\circ} <$ 