  Some different correlations between optical-UV variability and other quasar
properties, such as luminosity, black hole mass and rest-frame wavelength, were
discovered. The positive correlation between optical-UV variability amplitude
and black hole mass was first found by Wold et al., and this was confirmed by
Wilhite et al. We suggest that the accretion disk model can explain these
correlations, provided the optical-UV variability is triggered by the change of
accretion rate. The disk temperature of accretion discs decreases with
increasing black hole mass, which leads to systematical spectral shape
difference with black hole mass even if the black hole is accreting at the same
rate m_dot (m_dot = M_dot / M_dotEdd). The observed positive correlation
between optical-UV variability and black hole mass can be well reproduced by
our model calculations, if the mean accretion rate m_dot0 ~ 0.1 with variation
of m_delta ~ 0.4 - 0.5 m_dot0. We also found that the observed correlations of
optical-UV variability amplitude with luminosity or rest-frame wavelength can
be qualitatively explained by this accretion disc model.
