The case of the disappearing bias: A 2014 update to the “Gerrymandering or Geography” debate

Abstract

This note observes that the pro-Republican bias in the relationship between seats and votes that characterized the 2012 US congressional elections largely disappeared in the 2014 elections, where Republicans won a six-point victory in the national popular vote but only a handful of additional seats. Replicating analysis from an earlier article on the 2012 elections, I find that the source of the decline in bias supports two theories about the effects of gerrymandering and geography on the US Congress. First, bias declined most sharply in states where maps were drawn by Republicans, suggesting that these maps were drawn specifically to maximize seats during a tied national election environment. And second, pro-Republican bias present in bipartisan maps almost entirely disappears, as does the previously observed effect of urbanization on bias, further supporting existing theories about the asymmetric geographic dispersion of partisans.