Introducing the Reverse Gerrymandering Index: US House Elections 1872-2022

This paper presents a new measure of gerrymandering, called the Reverse Gerrymandering Index (RGIx). Unlike the efficiency gap and partisan symmetry measures, which are influenced by vote variation across the entire state or country, the mainstay of RGIx is that it estimates the gerrymandering level of each district by comparing its partisan vote distribution with the partisan vote distribution of the districts adjacent to it. From there, RGIx can be used to identify highly gerrymandered districts, measure regional or historical variation in gerrymandering, or as a variable in statistical models, to name just a few applications. It can also calculate gerrymandering scores for an unlimited number of parties per district, making it applicable to comparative electoral systems research. I use RGIx to show that gerrymandering began rising rapidly in federal elections in the 1960s, and that it began to shift dramatically in a pro-Republican direction starting in the 1980s.