Distribution of BI and AI for quasars detected as BAL by automatic procedures in previous SDSS releases, and that were not flagged by the visual inspection of the BOSS spectra. The black histogram shows the distribution of AI as measured by Trump et al. (2006) for 296 such quasars (all have BI = 0). About half of them are not real BALs (see text). From the automatic detection by Allen et al. (2011) (blue histogram), 57 quasars were missed by the visual inspection. Here again, only a handful of these objects actually display BAL troughs.