Star formation activity in the different regions explored in our sample (see legend). From top to bottom: (upper panel) number of protostars (P) with respect to the total amount of dense gas M_dense, (middle panel fraction of dense gas f_dense, and (lower panel) star formation efficiency in the dense gas (see the values in Table 1). We display the linear fit of all our targets (dashed red line) and their corresponding Pearson p-coefficients (see the values in legend) in the upper and middle panels.