that evolution LGRB host metallicity has a negligible effect up to z $\sim$ 2 which is consistent with the results of [first@refmzd,@]{}.](LGRB_num_stat_single.pdf){width=".49\textwidth"}

Rather surprisingly, as shown in [first@refredshift\_distribution,@]{}, we find that there does not appear to be any particularly significant differences in the redshift distributions of the different LGRB samples aside from the following:

1.  [@stats_paper] sample shows a considerably reduced rate of LGRB observation at redshifts high enough ([*z*]{} $\gtrsim$ 0.5) to require a separate IR spectrograph to observe some of the lines required for determining a metallicity. As X-Shooter contains an integrated IR spectrograph, the [@xshooter_survey] sample is not subject to this effect.

2.  The [@xshooter_survey] metallicity sample has a gap from 1.7 $\lesssim$ [*z*]{} $\lesssim$ 2.1 which is due to a confluence of observational limitations. The \[O II\] 3727 [Å]{} is redshifted to the optical IR transition at about 1 micron, the 4861 [Å]{} H$\beta$ and 4959 & 5007 [Å]{} \[O III\] lines are redshifted to a region of poor sky transmittance between J and H bands, and 6563 [Å]{} H$\alpha$ is redshifted into a similar low transmittance region between the H and K bands. We also find a smaller gap from 1.0 $\lesssim$ [*z*]{} $\lesssim$ 1.2 