  The scale factor $\sigma_{eff}$, which characterizes double parton collisions
in high energy hadron interactions, is a direct manifestation of the
distribution of the interacting partons in transverse space, in such a way that
different distributions give rise to different values of $\sigma_{eff}$ in
different double parton collision processes. We work out the value of the scale
factor in a few reactions of interest, in a correlated model of the
multi-parton density of the proton recently proposed.
