Mass-loss rates (from Eq. (3)) versus accretion rates Ṁ_acc of protostellar outflow sources at different evolutionary stages observed with a single Herschel/PACS footprint. Mass-outflow rates were determined assuming that the HM89 shock model conditions prevail. Geometric means for Class 0/I/II outflows are plotted as non-filled black markers. Thin coloured lines are contour lines based on a kernel-density estimate using Gaussian kernels.