The Oracle of Omaha is at it again. On July 7, Warren Buffett told Bloomberg: "I think the rich have a responsibility to pay higher tax rates." Then he groused that his wealthy friends are "paying lower tax rates than the people who are serving us the food." Mr. Buffett has been voicing this complaint for years, once observing that his personal tax rate of 17.7% is lower than that of his receptionist (30%).

During Monday night's national address, President Obama recited the Buffet line that millionaires and billionaires pay lower tax rates than their secretaries. Democrats in Congress routinely cite Mr. Buffett's tax confessions as irrefutable evidence that tax rates on the very rich are too low and the system is unfair. And the system would be unfair, if Mr. Buffett's tax facts were the whole truth. But they aren't.

I don't know the details of Warren Buffet's personal taxes, and he hasn't made them public. But the IRS does provide reliable data on effective tax rates—the overall share of their income that various groups pay in federal income taxes (not including state or local taxes) after accounting for all deductions and exemptions. These are different than marginal tax rates, which are paid on the next dollar of income and now peak at 35% for individuals.

IRS data for 2008, for example, show that households in the top 10% of earners (above about $114,000) paid 19% of their income to the feds. Those in the top 1% (above $380,000) paid 23.3%. The top 0.1% of earners, with incomes of $2 million or more, end up paying a slightly lower tax of 22.7%, because they get more of their income from investments (more about this below).