Scheme dependence, leading order and higher twist studies of MRST partons

We extend a recent global analysis of nucleon parton distributions carried out at next-to-leading order (NLO) in the <(MS)over bar> scheme to provide distributions in the so-called DIS scheme. We pay particular attention to t he translation of the heavy quark distributions in going from the <(MS)over bar> to the DIS scheme. We repeat the global analysis at leading order (LO ) and comment on the major effects produced when going from EO to NLO. Fina lly we include in the global analysis a freely parameterised form of possib le higher twist contributions to make an exploratory study of the size of t hese effects as a function of x. (C) 1998 Elsevier Science B.V. All rights reserved.