Supposed universality of 1/3 shot noise reduction

In coherent diffusive samples, a shot noise reduction factor of 1/3 results from the bimodal nature of the transmission probabilities. Further, a reduction factor of 1/3 has been found in the case of incoherent scattering, treated by the Boltzmann-Langevin equation. The occurence of the same 1/3 in both cases has been considered to be universal. Elaborating on an earlier discussion, it is demonstrated that the physics in the two cases is very different, and that the repeated occurrence of 1/3 is not a consequence of an underlying common mechanism.