We used tax filings and other records to track the political activity of 106 groups in their 2010 tax year. To calculate how much each group spent on elections, we added up spending they disclosed to federal and state election authorities, as well as donations made to political committees and grants to other social welfare groups that were earmarked for political ads.

We calculated each group’s percent of political spending in one of two ways. For groups that reported more political spending to the IRS than was reported in other records, we compared this to the total spending reported in their tax returns. Otherwise, we compared the spending reported in election records and elsewhere to the total expenditures in their tax returns.