Relation between the mass fraction of the stellar component forming a bound cluster after violent relaxation, F_bound, and the global SFE of the star-forming region. The solid (black) line, taken from Parmentier & Gilmore (2007), corresponds to a uniform local star formation efficiency (i.e. ϵ_3D(r) = SFE irrespective of r). The dashed and dash-dotted lines (blue and red) depict the models with radially varying star formation efficiencies of Adams (2000) (i.e. ϵ_3D(r) higher at smaller r than at large r). They build on either an isotropic (“I”, see key) or anisotropic (“A”) stellar velocity distribution.