  The freedom associated with the definition of parton distribution functions
is analyzed and formulae governing the dependence of parton distribution
functions and hard scattering cross-sections on unphysical quantities
associated with the renormalization and factorization procedure are derived.
The issue of the specification of factorization schemes via the corresponding
higher order splitting functions is discussed in detail. A numerical analysis
of the practical applicability of the so called ZERO factorization scheme,
which could be useful for the construction of consistent NLO Monte Carlo event
generators, is presented.
