Spectral variability of FIRST bright QSOs with SDSS observations
  For some samples, it has been shown that spectra of QSOs with low redshift
are bluer during their brighter phases. For the FIRST bright QSO sample, we
assemble their spectra from SDSS DR7 to investigate variability between the
spectra from White et al. (2000) and from the SDSS for a long rest-frame
time-lag, up to 10 years. There are 312 radio loud QSOs and 232 radio quiet
QSOs in this sample, up to $z \sim 3.5$. With two-epoch variation, it is found
that spectra of half of the QSOs appear redder during their brighter phases.
There is no obvious difference in slope variability between sub-samples of
radio quiet and radio loud QSOs. This result implies that the presence of a
radio jet does not affect the slope variability on 10-year timescales. The
arithmetic composite difference spectrum for variable QSOs is steep at blueward
of $\sim$ 2500\AA. The variability for the region blueward of 2500 \AA\ is
different to that for the region redward of 2500 \AA.
