a) Histogram distributions of the ionization parameter, estimated with the [O ii]/[O iii] ratio, for EELGs, green peas (GPs), and Hii galaxies. b) Relation between the oxygen abundance derived from the direct method and the [O iii] electron temperature, t_e[O iii], for the sample of giant Hii regions and nearby Hii galaxies from Pérez-Montero & Contini (2009, black points) and the sample of GPs from Amorín et al. (2010, green points). The red line indicates the best-fit to the data shown in Eq. (1). c) Comparison between the metallicity derived using the direct method and from the t_e[O iii] −Z calibration shown in Eq. (1) and their residuals d). Dashed lines in d) indicate the 2σ limits.