AGN Outflows in Emission and Absorption: The SDSS Perspective
  A variety of investigations have demonstrated commonalities between the Baldwin (1977) Effect, the blueshifting of CIV emission lines (e.g., Gaskell 1982; Richards et al. 2002), and the L_UV-L_X relationship (e.g., Avni & Tananbaum 1982; Strateva et al. 2005; Steffen et al. 2006); indeed all three of these observational effects may be manifestations of the same underlying (but still uncertain) physics. This commonality is of interest to investigations of accretion disk winds (e.g., Murray et al. 1995; Proga et al. 2000) from active galactic nuclei (AGN) as there is evidence that broad absorption line quasars (BALQSOs) are drawn from a parent sample of quasars that exhibit larger than average CIV blueshifts, weaker than average CIV emission line strengths, and bluer than average (intrinsic) colors. The properties of the absorption troughs appear to be dependent upon these parameters. Thus, it is suggested that not all quasars will host bona-fide BAL troughs, but that all (broad emission line) quasars host outflows of some type, the structure of which is strongly dependent on the quasar's spectral energy distribution. 
Gordon T. Richards