  An error was made when calculating the amplitude of the perturbed scalar mode
after Hubble-radius crossing. When corrected, it eliminates the leading term in
the statistical anisotropy of the power spectrum, reducing it from the
previously claimed upper estimate of $\lesssim 10^{-2}$ to the level of at most
$10^{-6}$, which is beyond the possibility of detection. The general conclusion
is that a single-field inflationary scenario cannot produce statistical
anisotropy of appreciable magnitude.
