Stellar mass – oxygen abundance relation for the same samples as in Fig. 4 shown by the same symbols. For comparison, the SDSS DR7 emission-line galaxy sample from Izotov et al. (2014), where the errors of the [O iii]λ4363 emission-line fluxes do not exceed 25%, are shown by black dots with the linear likelihood regression for these data plotted by a solid black line. The location of high-redshift star-forming galaxies is shown by various large green symbols (see text).