or lost its outer hydrogen and helium layers [@Woosley1993; @Woosley; @Langer].

To understand how LGRBs seem to have a metallicity aversion despite the existence of counterexamples, [@stats_paper] compared the metallicity distribution of the hosts of LGRBs with that of the hosts of several similar indicators of star-formation: LGRBs, Type Ic-bl, and Type II SNe as well as with the metallicity distribution of star-formation in the general galaxy population of the local universe. [@stats_paper] found that three quarters of the LGRB host population have metallicities below 12+log(O/H) $<$ 8.6 (in the @KobulnickyKewley KK04 metallicity scale), while less than a tenth of local star-formation is at similarly low metallicities. However, the supernovae were statistically consistent with the metallicity distribution of star-formation in the general galaxy population. While the LGRB sample did extend to higher redshifts than the other populations the observed metallicity difference was far too great to be a product of metallicity evolution. [@stats_paper] concluded that a low metallicity environment must be a fundamental component of the evolutionary process that forms LGRBs.

[@diff_rate_letter] expanded on the analysis of [@stats_paper] by comparing the metallicity distribution of LGRB host galaxies to the that of star forming galaxies in the local universe. By effectively 