  Spectral functions do not fully describe quasielastic electron and neutrino
scattering from nuclei because they only model the initial state. Final state
interactions distort the shape of the differential cross section at the peak
and increase the cross section at the tails of the distribution. We show that
the kinematic distributions predicted by the $\psi'$ superscaling formalism can
be well described with a modified {\it {effective spectral function}} (ESF). By
construction, models using ESF in combination with the transverse enhancement
contribution correctly predict electron QE scattering data. Our values for the
binding energy parameter $\Delta$ are smaller than $\overline{\epsilon}$
extracted within the Fermi gas model from pre 1971 data by Moniz, probably
because these early cross sections were not corrected for coulomb effects.
