  We have studied numerically the fluctuations of the conductance, $g$, in
two-dimensional, three-dimensional and four-dimensional disordered
non-interacting systems. We have checked that the variance of $\ln g$ varies
with the lateral sample size as $L^{2/5}$ in three-dimensional systems, and as
a logarithm in four-dimensional systems. The precise knowledge of the
dependence of this variance with system size allows us to test the
single-parameter scaling hypothesis in three-dimensional systems. We have also
calculated the third cumulant of the distribution of $\ln g$ in two- and
three-dimensional systems, and have found that in both cases it diverges with
the exponent of the variance times 3/2, remaining relevant in the large size
limit.
