Can we improve CIV-based single epoch black hole mass estimations?
  In large optical survey at high redshifts ($z>2$), the CIV broad emission
line is the most practical alternative to estimate the mass ($M_{\text{BH}}$)
of active super-massive black holes (SMBHs). However, mass determinations
obtained with this line are known to be highly uncertain. In this work we use
the Sloan Digital Sky Survey Data Release 7 and 12 quasar catalogues to
statistically test three alternative methods put forward in the literature to
improve CIV-based $M_{\text{BH}}$ estimations. These methods are constructed
from correlations between the ratio of the CIV line-width to the low ionization
line-widths (H$\alpha$, H$\beta$ and MgII) and several other properties of
rest-frame UV emission lines. Our analysis suggests that these correction
methods are of limited applicability, mostly because all of them depend on
correlations that are driven by the linewidth of the CIV profile itself and not
by an interconnection between the linewidth of the CIV line with the linewidth
of the low ionization lines. Our results show that optical CIV-based mass
estimates at high redshift cannot be a proper replacement for estimates based
on IR spectroscopy of low ionization lines like H$\alpha$, H$\beta$ and MgII
