the metallicity-independent DTD); however, the qualitative effects of the models that we have considered are already sufficiently evident.

Discussion and Conclusions {#section:vi}
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The rate of Type Ia supernovae should be affected at some level by the effects of metallicity on stellar evolution. There may be various complications involved, such as the largely unresolved effects of binary evolution, but our simple model for the effects of metallicity should be broadly relevant. There has been significant effort devoted to investigating Type Ia SN properties as a function of metallicity (e.g., @Hamuy:2000ya [@Gallagher:2008zi; @Howell:2008jv; @Neill:2009tr; @Sullivan:2010mg; @Konishi:2011ct]). Since the properties of SN Ia have been seen to depend on metallicity, why not the rate?

The simple models that we have considered explain fairly well both the specific SN Ia rates measured in nearby galaxies by LOSS and the observed normalization and evolution of the cosmic SN Ia rate. Further progress can certainly be made with data that can break the degeneracy between decreasing metallicity and decreasing age. Indeed, evidence in this direction has been found in a comparison of SN Ia host galaxies in SDSS by @Cooper:2009vk, who found that SNe Ia in blue, star-forming hosts have a preference for lower-density environments, 