rather than SFR is also beneficial for calibrating the relationship between the strong line ratios and ${\hbox{(O/H)$_{\rm T_e}$}}$. Figure \[fig:dssfr\] shows that at a fixed strong line ratio, there is significant scatter in ${\hbox{$M_{\star}$}}$. Since ${\hbox{$M_{\star}$}}$ and SFR are correlated, absolute SFR does not necessarily correspond to a lower oxygen abundance at a fixed strong line value. Furthermore, since ${\hbox{$\Delta\log$(SSFR)}}$ is a reflection of the SFR density, galaxies with similar ${\hbox{$\Delta\log$(SSFR)}}$ ought to have similar ionization conditions. The same does not hold true for galaxies with similar SFR but different stellar masses, since a relatively low mass, compact star forming galaxy will have more intense ionization conditions than a more massive galaxy with relatively diffuse star formation.

Our choice of bin widths was largely *ad hoc*. It is clear from Figure 11 of @Andrews13 that there is some scatter in ${\hbox{(O/H)$_{\rm T_e}$}}$ at fixed ${\hbox{$M_{\star}$}}$ and ${\hbox{$\Delta\log$(SSFR)}}$. Our primary motives were to (1) resolve the ${\hbox{$M_{\star}$--$Z$--${\rm SFR}$}}$ relationship, (2) include enough galaxies in metal rich stacks to measure ${\hbox{(O/H)$_{\rm T_e}$}}$, and (3) limit the total number of stacks to keep the stacking procedure, stellar continuum subtraction, and abundance determination computationally feasible. We ran various trials and found our results to 