If one retains M^2/Q^2 terms in the kinematics, the Nachtmann variable \xi
seems to be more appropriate to describe deep inelastic lepton-nucleon
scattering. Up to the first power of M^2/Q^2, a modified Wandzura-Wilczek
relation with respect to \xi was derived. Kinematical correction factors are
given as functions of \xi and Q^2. A comparison of the modified g_2^WW(\xi) and
original g_2^WW(x) with the most recent g_2 data is shown.Comment: 10 pages, 3 figures, revised version with minor correction
