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"Nonpartisan, independent and nonprofit, OpenSecrets is the nation's premier research group tracking money in U.S. politics and its effect on elections and public policy. Our mission is to track the flow of money in American politics and provide the data and analysis to strengthen democracy."

This was a study of the money spent by political advocacy groups during the 2000-2006 election cycles. While historical, it provides an interesting window into the influence this money has on the election cycle. This is money that is not controlled under federal campaign finance law.