  A theory of the probability distribution function (PDF) tails of the blob
density in plasma edge turbulence is provided. A simplified model of the fast
convective radial transport is used. The theoretically predicted PDF tails
corroborate earlier measurements of edge transport, further confirming the
strongly non-Gaussian feature of edge transport. It is found that increasing
the cross sectional spatial scale length ($L_x$ and $L_y$) of the blob results
in larger transport whereas increasing the toroidal scale length ($L_z$)
decreases the PDF. The results imply that the PDF decreases for larger blob
speed $v_b$.
