Using the Properties of Broad Absorption Line Quasars to Illuminate
  Quasar Structure
  A key to understanding quasar unification paradigms is the emission
properties of broad absorption line quasars (BALQs). The fact that only a small
fraction of quasar spectra exhibit deep absorption troughs blueward of the
broad permitted emission lines provides a crucial clue to the structure of
quasar emitting regions. To learn whether it is possible to discriminate
between the BALQ and non-BALQ populations given the observed spectral
properties of a quasar, we employ two approaches: one based on statistical
methods and the other supervised machine learning classification, applied to
quasar samples from the Sloan Digital Sky Survey. The features explored include
continuum and emission line properties, in particular the absolute magnitude,
redshift, spectral index, line width, asymmetry, strength, and relative
velocity offsets of high-ionisation CIV $\lambda 1549$ and low-ionisation MgII
$\lambda 2798$ lines.
  We consider a complete population of quasars, and assume that the statistical
distributions of properties represent all angles where the quasar is viewed
without obscuration. The distributions of the BALQ and non-BALQ sample
properties show few significant differences. None of the observed continuum and
emission line features are capable of differentiating between the two samples.
Most published narrow disk-wind models are inconsistent with these
observations, and an alternative disk-wind model is proposed. The key feature
of the proposed model is a disk-wind filling a wide opening angle with multiple
radial streams of dense clumps.
