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Political Science

Matthew Yglesias (June 03, 2008) - The Math (Politics)

Matthew Yglesias writes:

The Math: hart borrowed from David Park relates the share of the vote going to Democrats to the share of House seats controlled by Democrats. You can see that starting in 1994 we entered an era when Democrats have consistently underperformed their vote share. If the current Democratic majority can stay in place past the 2010 census, one assumes that will change. Still, it should always be remembered -- but especially in these days of heady optimism -- that the structure of American political institutions provides a substantial bias in favor of conservatism and makes it difficult for small progressive majorities to accomplish very much.

Perhaps the most interesting thing about the graph is this: there is exactly one election since 1930 in which more Americans voted for the Republicans than for the Democrats. Only in 1994 did Republicans win the two-party vote share. Yet the House has been Republican-majority in 8 of 31 post-WWII congresses.

Two things seem to be going on in the relationship between the two lines. First, there is a magnification effect--a 1% swing in the vote share leads to a greater than 1% swing in the number of seats. Second, more often than not there appears to be a Republican bias: a 50-50 vote share House would, in almost every year, be a Republican-majority House.

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