Correction

A line in the March 2012 Harper’s Index incorrectly stated that 72 percent of political ad spending during the 2010 election cycle would have been prohibited before the Supreme Court’s Citizens United decision. In fact, 72 percent of outside political ad spending in the 2010 cycle would have been prohibited before Citizens United and a 2007 decision, Federal Election Commission v. Wisconsin Right to Life, Inc. Although the item was sourced to the Center for Responsive Politics, the mistake was entirely ours. We regret the error.