Panel a: semi-direct Z_Te deficit (as defined in Sect. 5.2) as a function of O⁺⁺/O⁺. There is a tight anti-correlation between these two properties at low values of O⁺⁺/O⁺. Panel b: semi-direct Z_Te deficit as a function of the nebular line ratio [OIII]/[OII]. As in Fig. 4, the Bayesian fit to this relation is given by the solid dark grey line, and the least-squares fit is given by the solid black line. These fits can be used to help correct semi-direct Z_Te estimates for the O⁺⁺/O⁺ bias seen in panela.