Emission line ratios as a function of the intrinsic oxygen abundance for the sample data (black dots). The blue and pink dashed lines represent the best fits to the simulated data, considering synthetic spectra non-attenuated and attenuated by the Calzetti law, respectively. The shaded regions shows the 95% prediction intervals. The red dots in the last panel represent the attenuated data by the Calzetti law. The metallicity range of applicability of each literature calibration is reflected in the length of each relation.