When Mitt Romney claims, as he did in a private talk at a fundraiser for well-heeled donors, that 47 percent of Americans do not pay income taxes, where can one check his math? When President Barack Obama tells David Letterman and his audience that he doesn't know how much the national debt is, what's the best place to get the latest number? When a member of Congress claims federal spending has been cut to the bone, what's the best place to check that claim?

Investigative Reporters and Editors and the Sunlight Foundation are launching Econocheck, a new ...