  We use 12000 stars from Large Sky Area Multi-Object Fiber Spectroscopic
Telescope (LAMOST) spectroscopic data to show that the metallicities of Kepler
field stars as given in the Kepler Input Catalog (KIC) systematically
underestimate both the true metallicity and the dynamic range of the Kepler
sample. Specifically, to the first order approximation, we find [Fe/H]_KIC =
-0.20 + 0.43 [Fe/H]_LAMOST, with a scatter of ~0.25 dex, due almost entirely to
errors in KIC. This relation is most secure for -0.3<[Fe/H]_LAMOST<+0.4 where
we have >200 comparison stars per 0.1 dex bin and good consistency is shown
between metallicities determined by LAMOST and high-resolution spectra. It
remains approximately valid in a slightly broader range. When the relation is
inverted, the error in true metallicity as derived from KIC is (0.25
dex)/0.43~0.6 dex. We thereby quantitatively confirm the cautionary note by
Brown et al. (2011) that KIC estimates of [Fe/H] should not be used by "anyone
with a particular interest in stellar metallicities". Fortunately, many more
LAMOST spectroscopic metallicities will be available in the near future.
