  We present a spectral-variability analysis of the low-redshift quasar PDS 456
using principal component analysis. In the XMM-Newton data, we find a strong
peak in the first principal component at the energy of the Fe absorption line
from the highly blueshifted outflow. This indicates that the absorption feature
is more variable than the continuum, and that it is responding to the
continuum. We find qualitatively different behaviour in the Suzaku data, which
is dominated by changes in the column density of neutral absorption. In this
case, we find no evidence of the absorption produced by the highly ionized gas
being correlated with this variability. Additionally, we perform simulations of
the source variability, and demonstrate that PCA can trivially distinguish
between outflow variability correlated, anti-correlated, and un-correlated with
the continuum flux. Here, the observed anti-correlation between the absorption
line equivalent width and the continuum flux may be due to the ionization of
the wind responding to the continuum. Finally, we compare our results with
those found in the narrow-line Seyfert 1 IRAS 13224-3809. We find that the Fe K
UFO feature is sharper and more prominent in PDS 456, but that it lacks the
lower energy features from lighter elements found in IRAS 13224-3809,
presumably due to differences in ionization.
