  It is proposed that the rate of relaxation in a liquid is better described by
the geometric mean of the van Hove distribution function, rather than the
standard arithmetic mean used to obtain the mean squared displacement. The
difference between the two means is shown to increase significantly with an
increase in the non-Gaussian character of the displacement distribution.
Preliminary results indicate that the geometric diffusion constant results in a
substantial reduction of the deviation from Stokes-Einstein scaling.
