Dec $< 1.25^{\circ}$).

For the SDSS DR7Q, since the Stripe 82 imaging is deeper we are able to select quasars to $i<19.9$ for the cross-correlation study. We further restrict our analysis to SDSS DR7 quasars in the redshift range $0.15<z<2.5$, with a median redshift of 1.4. The redshift cut is used to avoid the redshift deserts of quasars at $z\sim2.7$ and $\sim3.5$ due to contamination from F and GK stars (Fan 1999; Richards et al. 2002, 2006).

One complication for SDSS-III BOSS DR9 is that a set of quasar selection methods, and not the uniform XDQSO method, was used in the Stripe 82 region. Consequently, the White et al. (2012) completeness corrections are not suitable in Stripe 82. However, during BOSS observations, Stripe 82 was observed at a high target density (Palanque-Delabrouille et al. 2011) and the actual completeness of $2.2<z<3.5$ quasars is close to $100\%$, down to the $g\leq22.0$ or $r\leq21.85$ limiting magnitude (Palanque-Delabrouille et al. 2013; Ross et al. 2013).

### Quasar Redshift and Luminosity distributions

  Region                         DR7     DR9
  ------------------------------ ------- -----------
  HeRS (79 deg$^2$)              1,411   630 (762)
  HeLMS (270 deg$^2$)            1,675   769 (947)
  Boötes (11.3 deg$^2$)          100     183
  Lockman-SWIRE (15.2 deg$^2$)   153     -
  [*XMM*]{}-LSS (21.6 deg$^2$)   -       