Votes and Seats: What Made the 2012 Election Different

by John Sides on November 12, 2012 · 6 comments

in Campaigns and elections


Apropos of Dan’s earlier post, political scientist Matthew Green sends the graph above and writes:
If the numbers reported by Aaron Blake in the Washington Post are correct, it would be highly unusual, historically speaking.

The chart shows, for every election since 1962, the percent of the two-party vote that all Democratic House candidates received ( horizontal axis) compared with the percent of House seats that Democratic candidates actually won (vertical axis).  Leaving aside 2012, for which the data are still tentative, in only one election during this 50 year period (1996) did a party that received a majority of the two-party popular vote fail to win a majority of seats in the House.

What is true, however, is that the winning party has almost always gotten an extra boost in House seats.  With two exceptions—the 1994 and 2006 elections—the party that has received a majority of the popular vote won a larger share of House seats.

In fact, that extra boost used to be much bigger than it is today.  Between 1962 and 1992, the majority party (always the Democratic Party) won an average of seven percentage points more House seats than their share of the two-party vote.  But from 1994 to 2010, that difference was a mere 1.1 percentage points.

Of course, within individual states there may be large discrepancies between the popular vote and seat share (see e.g. Pennsylvania in this election cycle).  But despite—or perhaps because of?—the rise of sophisticated gerrymandering by both parties over the past two decades, the House has become more, not less, representative of the popular vote.

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