instance, the \[\] $\lambda$ 3727 Å line requires a significantly higher energy to excite than the \[\] $\lambda$6583 Å line [@Pilyugin10]. As a result, nitrogen based diagnostics can serve as indicators of the oxygen abundance.

Many strong-line calibrations are often inconsistent with one another. @Kewley08 show the extent to which the various strong line calibrations disagree and provide a framework for mapping one strong line metallicity onto another. Many of the strong-line calibrations differ simply because they use different calibration samples, but the situation is more complicated than sample selection. Some calibrations utilize grids from photoionization simulations [@McGaugh91; @Zaritsky94; @Kewley02], while others use unique samples of regions [e.g., @Marino13] which themselves are often heterogeneous compilations of samples from the literature [e.g., @Pettini04; @Pilyugin10].

Empirical abundance diagnostics have the benefit of being calibrated on direct method measurements, but due to selection effects the calibration samples are often biased toward low metallicity regions [@Jones15]. The application of these calibrations to integrated spectra of moderately star forming galaxies requires significant extrapolation from the regions that compose most calibration samples. Furthermore, most empirical calibrations will result in erroneous metallicities if, for instance, the ionization conditions of the galaxies in question differ significantly from the 