  We revise the Kubo formula for the electric dc conductivity in the presence
of spin-orbit coupling (SOC). We discover that each velocity operator that
enters this formula differs from $\partial H/\partial \boldsymbol p$, where $H$
is the Hamiltonian and $\boldsymbol p$ is the canonical momentum. Moreover, we
find an additional contribution to the Hall dc conductivity from noncommuting
coordinates that is missing in the conventional Kubo-Streda formula. This
contribution originates from the "electron-positron" matrix elements of the
velocity and position operators. We argue that the widely used Rashba model
does in fact provide a finite anomalous Hall dc conductivity in the metallic
regime (in the noncrossing approximation) if SOC-corrections to the velocity
and position operators are properly taken into account. While we focus on the
response of the charge current to the electric field, linear response theories
of other SOC-related effects should be modified similarly.
