  It is shown that the distribution functions of the diffusion coefficient are
very similar in the standard model of quantum diffusion in a disordered metal
and in a model of classical diffusion in a disordered medium: in both cases the
distribution functions have lognormal tails, their part increasing with the
increase of the disorder. The similarity is based on a similar behaviour of the
high-gradient operators determining the high-order cumulants. The one-loop
renormalization-group corrections make the anomalous dimension of the operator
that governs the $s$-th cumulant proportional to $s(s-1)$ thus overtaking for
large $s$ the negative normal dimension. As behaviour of the ensemble-averaged
diffusion coefficient is quite different in these models, it suggests that a
possible universality in the distribution functions is independent of the
behaviour of average quantities.
