  Probability Distributions Functions (PDFs) of fluctuations of plasma edge
parameters are skewed curves fairly different from normal distributions, whose
shape appears almost independent of the plasma conditions and devices. We start
from a minimal fluid model of edge turbulence and reformulate it in terms of
uncoupled Langevin equations, admiting analytical solution for the PDFs of all
the fields involved. We show that the supposed peculiarities of PDFs, and their
universal character, are related to the generic properties of Langevin
equations involving quadratic nonlinearities.
