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Average Ideology of the House and Senate, 1947 - 2012

The following graphics show the average ideology of the Republican and Democratic parties in Congress since World War II. In recent years, the Republican party has become far more conservative than the Democratic party has become liberal. The average ideology of the House has likewise become more conservative; this shift began during the 104th Congress.

This data was compiled from Tables 8-9 and 8-10 in Vital Statistics on Congress

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Vital StatsAbout Vital Statistics on Congress

For more than three decades, Vital Statistics on Congress, a joint effort undertaken by Norm Ornstein of the American Enterprise Institute and Tom Mann of Brookings in collaboration with Michael Malbin of the Campaign Finance Institute, has been a go-to reference guide for Congressional watchers for impartial data on Congress and its members.

Vital Statistics’ purpose has always been to collect useful data on our first branch of government – in the election and composition of its membership as well as its formal procedure, such as the use of the filibuster, informal norms, party structure and staff. This dataset also documents the increasing polarization of Congress and the demographics of those who serve in the U.S. Senate and U.S. House of Representatives.

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