  By probabilistic means, the concept of contextuality is extended so that it
can be used in non-ideal situations. An inequality is presented, which at least
in principle enables a test to discard non-contextual hidden-variable models at
low error rates, in the spirit of the Kochen-Specker theorem. Assuming that the
errors are independent, an explicit error bound of 1.42% is derived, below
which a Kochen-Specker contradiction occurs.
