Estimating the Partisan Consequences of Redistricting Plans-Simply

Abstract

Although some judges and political scientists have recently doubted that it is possible to predict the partisan consequences of redistricting plans, I demonstrate that it is simple to do so with a pair of OLS equations that regress voting percentages on major party registration percentages. I test this model on data for all California Assembly and Congressional elections from 1970 through 1992, and compare it to logit results and to more complicated equations that contain incumbency and socioeconomic variables. Since information on socioeconomic variables is often not available early in a redistricting cycle, and since incumbency in a district is often difficult to determine precisely after a reapportionment, I rely on the simplest equation, which correctly predicts 90% of the results. I show that analogous equations using registration or votes for minor or even major offices in California, North Carolina, and Texas can predict outcomes with considerable accuracy. Using the party registration equations, I show that the so-called Burton Gerrymander of 1980 had minimal partisan consequences, while the nonpartisan plan instituted by the California Supreme Court's Special Masters in 1992 was nearly as biased in favor of the Republicans as the proposal of the Republican party, which would have insured the GOP a majority of the Congressional seats even if Democrats won a landslide of the votes. I conclude by introducing a new graphical representation of redistricting plans, which strongly implies that in 1991, Republican and Democratic line drawers in California agreed on the registration margins necessary for party control and drew their plans with these in mind.