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A key to understanding quasar unification paradigms is the emissionproperties of broad absorption line quasars (BALQs). The fact that only a smallfraction of quasar spectra exhibit deep absorption troughs blueward of thebroad permitted emission lines provides a crucial clue to the structure ofquasar emitting regions. To learn whether it is possible to discriminatebetween the BALQ and non-BALQ populations given the observed spectralproperties of a quasar, we employ two approaches: one based on statisticalmethods and the other supervised machine learning classification, applied toquasar samples from the Sloan Digital Sky Survey. The features explored includecontinuum and emission line properties, in particular the absolute magnitude,redshift, spectral index, line width, asymmetry, strength, and relativevelocity 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 statisticaldistributions of properties represent all angles where the quasar is viewedwithout obscuration. The distributions of the BALQ and non-BALQ sampleproperties show few significant differences. None of the observed continuum andemission line features are capable of differentiating between the two samples.Most published narrow disk-wind models are inconsistent with theseobservations, and an alternative disk-wind model is proposed. The key featureof the proposed model is a disk-wind filling a wide opening angle with multipleradial streams of dense clumps.

Using the Properties of Broad Absorption Line Quasars to Illuminate Quasar Structure