Does SEGUE/SDSS indicate a dual Galactic halo?
  We re-examine recent claims of observational evidence for a dual Galactic
halo in SEGUE/SDSS data, and trace them back to improper error treatment and
neglect of selection effects. In particular, the detection of a vertical
abundance gradient in the halo can be explained as a metallicity bias in
distance. A similar bias, and the impact of disk contamination, affect the
sample of blue horizontal branch stars. These examples highlight why non-volume
complete samples require forward-modelling from theoretical models or extensive
bias-corrections. We also show how observational uncertainties produce the
specific non-Gaussianity in the observed azimuthal velocity distribution of
halo stars, which can be erroneously identified as two Gaussian components. A
single kinematic component yields an excellent fit to the observed data, when
we model the measurement process including distance uncertainties. Furthermore,
we show that sample differences in proper motion space are the direct
consequence of kinematic cuts, and are enhanced when distance estimates are
less accurate. Thus, their presence is neither a proof for a separate
population, nor a measure of reliability for the applied distances. We conclude
that currently there is no evidence from SEGUE/SDSS that would favour a dual
Galactic halo over a single halo full of substructure.
