We investigate the behavior of spin-dependent parton distribution functions
(PDFs) at large parton momentum fractions x in the context of global QCD
analysis. We explore the constraints from existing deep-inelastic scattering
data, and from theoretical expectations for the leading x -> 1 behavior based
on hard gluon exchange in perturbative QCD. Systematic uncertainties from the
dependence of the PDFs on the choice of parametrization are studied by
considering functional forms motivated by orbital angular momentum arguments.
Finally, we quantify the reduction in the PDF uncertainties that may be
expected from future high-x data from Jefferson Lab at 12 GeV.Comment: 14 pages, 3 figures, 1 tabl
