Top panel: three-dimensional star formation efficiency, ϵ_3D, in dependence of the initial gas volume density, ρ₀. The clump edge is on the left, the clump centre on the right. The two vertical lines mark the limits of the p₀ = 1.5 model. Bottom panel: two-dimensional star formation efficiency, ϵ_2D, in dependence on the residual gas surface density, Σ_g. The plain squares depict the measurements of Gutermuth et al. (2011). In both panels, the models are identical to those in Figs. 10 and 11.