comparison of metallicity values requires that they be determined using as consistent a method as possible. Therefore we recalculate the [@xshooter_survey] metallicities, from their published flux values, to give R$_{23}$ metallicity values in the KK04 scale, using the exact same code as used to determine the metallicities given in [@stats_paper]. The measured metallicity values used in this work are given in [first@refxsd\_data\_table,@]{}.

Specifically to calculate metallicities we, as in [@stats_paper], employ an improved version of the idl code outlined in [@kd2002] which has been updated to the KK04 scale developed in [@KobulnickyKewley]. In order to correlate the flux of a line belonging to an individual atomic ionization level with the total abundance of that element it is necessary to know what fraction of the element is ionized to the level in question. This is achieved by measuring the flux ratio between the \[O II\] and \[O III\] line strength, giving the relative population in the O II and O III ionization states, and fitting the metallicity for that specific ionization state ratio. In the classical application of this diagnostic, an R$_{23}$ value would be calculated from the measured line ratios (using $R_{23} = {I_{3727} + I_{4959} + I_{5007} \over I_{H\beta}}$) 