The underlying driver for the \civ Baldwin effect in QSOs with $0<z<5$
  Broad emission lines is a prominent property of type I quasi-stellar objects
(QSOs). The origin of the Baldwin effect for \civ $\lambda1549~$\AA\ broad
emission lines, i.e., the luminosity dependence of the \civ equivalent width
(EW), is not clearly established. Using a sample of 87 low-$z$ Palomar-Green
(PG) QSOs and 126 high-$z$ QSOs across the widest possible ranges of redshift
($0<z<5$), we consistently calculate \hb-based single-epoch supermassive black
hole (SMBH) mass and the Eddington ratio to investigate the underlying driver
of the \civ Baldwin effect. An empirical formula to estimate the host fraction
in the continuum luminosity at 5100 \AA\ is presented and used in \hb-based
\mbh calculation for low-$z$ PG QSOs. It is found that, for low-$z$ PG QSOs,
the Eddington ratio has strong correlations with PC1 and PC2 from the principal
component analysis, and \civ EW has a strong correlation with the optical \feii
strength or PC1. Expanding the luminosity range with high-$z$ QSOs, it is found
that \civ Baldwin effect exists in our QSOs sample. Using \hb-based
single-epoch SMBH mass for our QSOs sample, it is found that \civ EW has a
strong correlation with the Eddington ratio, which is stronger than that with
the SMBH mass. It implies that the Eddington ratio seems to be a better
underlying parameter than the SMBH mass to drive the \civ Baldwin effect.
