The Reapportionment Revolution and Bias in U.S. Congressional Elections

We develop a simple formal model of the redistricting process that highlights the importance of two factors: first, partisan or bipartisan control of the redistricting process; second, the nature of the reversionary outcome, should the state legislature and governor fail to agree on a new districting plan. Using this model, we derive various predictions about the levels of partisan bias and responsiveness that should be observed under districting plans adopted under various constellations of partisan control of state government and reversionary outcomes, testing our predictions on postwar (1946{70) U.S. House electoral data. We find strong evidence that both partisan control and reversionary outcomes systematically affect the nature of a redistricting plan and the subsequent elections held under it. Further, we show that the well-known disappearance circa 1966 of what had been a long-time pro-Republican bias of about 6% in nonsouthern congressional elections can be explained completely by the changing composition of northern districting plans.