  We analyze the average of weak values over statistical ensembles of pre- and
post-selected states. The protocol of weak values, proposed by Aharonov et al.,
is the result of a weak measurement conditional on the outcome of a subsequent
strong (projective) measurement. Weak values can be beyond the range of
eigenvalues of the measured observable and, in general, can be complex numbers.
We show that averaging over ensembles of pre- and post-selected states reduces
the weak value within the range of eigenvalues of the measured operator. We
further show that the averaged result expressed in terms of pre- and
post-selected density matrices, allows us to include the effect of decoherence.
