At the request of the Center for Public Integrity, the nonpartisan Center for Responsive Politics, which tracks campaign finance data, used rigorous matching methods to compare publicly disclosed donors to 2016 presidential campaign committees with information about publicly disclosed donors to federal candidates dating back to the 2008 election cycle.

In addition, the Center for Responsive Politics was able to match some donor information dating back as far as 1990 election cycle. Campaign finance data is imperfect and donors’ personal information can change over time, making matching difficult, but the analysis used the best techniques available.

Campaigns must disclose information about donors who have given at least $200. Information about donors who give less than $200 is not publicly disclosed, making it impossible to include such donors in the analysis.