(see the right panel of Figure \[fig:BPT\]).

The N2 diagnostic is subject to biases caused by the ionization parameter as well as the hardness of the ionization spectrum [@Kewley02], but has been shown to be a useful abundance diagnostic in high excitation regions [@TSB94; @Binette96; @Pettini04; @Marino13]. Furthermore, \[\] $\lambda$ 6583 and ${\hbox{H$\alpha$}}$ are closely spaced, making their ratio insensitive to variations in reddening corrections. The O3N2 diagnostic is also sensitive to ionization parameter [@Kewley02], but is less sensitive to variations in the hardness of the ionizing spectrum than N2 [@Kewley13a; @Brown14; @Steidel14]. N2O2 is insensitive to ionization parameter, but is dependent on the secondary nature of nitrogen [@Kewley02]. We will use N2O2 to estimate the effect of ionization parameter variations on the other diagnostics.

With the above considerations in mind, we focus the remainder of our analysis on the N2, O3N2, and N2O2 strong line diagnostics. As discussed above, the distribution of ${\hbox{$R_{23}$}}$ at fixed ${\hbox{$M_{\star}$}}$ and ${\hbox{$\Delta\log$(SSFR)}}$ is not strongly peaked. Furthermore, the double valued nature of ${\hbox{$R_{23}$}}$ requires that an additional diagnostic sensitive to ionization parameter be used in conjunction with an iterative method to solve for an oxygen abundance. This precludes the empirical nature of our 