  Combining data on unpolarized and polarized inclusive proton structure
functions, we perform the first detailed study of quark-hadron duality in
individual helicity-1/2 and 3/2 virtual photoproduction cross sections. We find
that duality is realized more clearly in the helicity-1/2 channel, with duality
violating corrections < 10% over the entire nucleon resonance region, while
larger, < 20% corrections are found in the helicity-3/2 sector. The results are
in general agreement with quark model expectations, and suggest that data above
the Delta resonance region may be used to constrain both spin-averaged and
spin-dependent parton distributions.
