dividing one distribution by the other, [@diff_rate_letter] was able to directly determine the relative rate of LGRB formation as a function of metallicity in the low-redshift universe. They found a dramatic cutoff in the LGRB formation rate per unit star-formation above a metallicity of $ {\rm log(O/H)}+12 \approx 8.3 $ (in the @KobulnickyKewley scale), with LGRBs forming between ten and fifty times more frequently per unit star-formation below this cutoff than above.

[@xshooter_survey] performed a detailed analysis of 96 LGRB host galaxies with ESO Very Large Telescope (VLT) X-Shooter emission-line spectroscopy, providing the largest spectroscopic sample of LGRB host galaxies and comprising most of the publicly available data at the time. [@xshooter_survey] finds that at z $<$ 1 $\sim$20% of their LGRB host galaxies have super-solar metallicities a result comparable with [@stats_paper]. [@xshooter_survey] concludes that the properties of LGRB hosts can be explained by the tendency of LGRB events to avoid metal-rich environments.

[@Vergani2015] estimated the host stellar masses of the 14 z $<$ 1 BAT6 [@BAT6] host galaxies via spectral energy distribution (SED) fitting and found that those LGRBs tend to avoid massive galaxies in preference for faint low-mass star-forming galaxies typically below galaxy survey completeness limits. [@Vergani2015] estimates 