  QCD sum rules of the nucleon channel are reanalyzed, using the maximum
entropy method (MEM). This new approach, based on the Bayesian probability
theory, does not restrict the spectral function to the usual "pole +
continuum"-form, allowing a more flexible investigation of the nucleon spectral
function. Making use of this flexibility, we are able to investigate the
spectral functions of various interpolating fields, finding that the nucleon
ground state mainly couples to an operator containing a scalar diquark.
Moreover, we formulate the Gaussian sum rule for the nucleon channel and find
that it is more suitable for the MEM analysis to extract the nucleon pole in
the region of its experimental value, while the Borel sum rule does not contain
enough information to clearly separate the nucleon pole from the continuum.
