Molecular ratios MF/DE (upper panel), MF/EC (middle panel), and DE/EC (lower panel) as a function of the luminosity of the sources. The results found in this work (Table 11, black circles) are compared with a sample of different star-forming regions from literature (non-black coloured circles, see Table F.1 for references). Error bars are shown when available. The dashed black and red lines are the linear best-fits to the data of the sources included in this work and the hot corinos, respectively. For MF/EC, the large error bar of the lowest luminosity source of our sample (G14.33-0.65) results from the propagation of the high uncertainties of the individual column densities.