Core/condensation formation efficiency (CFE) as a function of the average densities of dense cores of similar sizes (FWHM  ~ 0.1 pc) but of different masses in Cygnus MDCs (filled symbols) and in ρ Ophiuchus (open triangles; Motte et al. 1998). The ρ Ophiuchus densities have been re-evaluated in the way we derived them in the present paper for a proper comparison. A transition from low efficiency cores to possible, single collapsing cores is observed from a few 10⁴ to a few 10⁶ cm^-3. The displayed ranges (uncertainty bars) for the Cygnus cores correspond to the range between the sums of M_PdBI and of M_env from Table 2. To help the clarity of the plot, the displayed location of CygX-N3 corresponds to its average density shifted by a factor of 1.1.