  Previously published data on inclusive neutral and charged current e+p and
e-p deep inelastic scattering from HERA have been combined. The new,
model-independent method of combining the measured cross sections takes full
account of correlated systematics in a coherent way, leading to significantly
reduced uncertainties in the combined measurement across the (x, Q^2) plane.
The combined cross section data have been used as the sole input for a new
next-to-leading order QCD fit to extract the parton distribution functions
(PDFs) of the proton. The PDFs extracted have greatly reduced experimental
uncertainties, compared to separate QCD analyses on data from H1 and ZEUS.
Model uncertainties, including those arising from the parameterisation
dependence, have also been carefully considered. The resulting HERA PDFs have
impressive precision.
