Mitt Romney is not alone. I thought Mr. Romney’s 13.9 percent federal tax rate would be hard to beat. But among the 400 Americans with the highest adjusted gross incomes in 2008, 30 of them paid less than 10 percent and another 101 paid less than 15 percent. And these people earned, on average, more than 10 times Mr. Romney’s $21.7 million — an average of $270.5 million each.

After I disclosed a few weeks ago that I pay 37 percent of my adjusted gross income and 74 percent of my taxable income in combined federal, state and local income and payroll taxes, I asked the Internal Revenue Service how that compares with other taxpayers. I never got a simple answer (and an I.R.S. spokesman said the agency could not discuss individual returns).

But this week, the I.R.S. sent me reams of data, including analyses of returns from taxpayers reporting adjusted gross income of more than $200,000 and returns from the top 400 taxpayers. Some data were from 2009, but most went back to 2008. (The agency offered no explanation as to why it takes so many years to compile.) But the data helps explain why many people are so angry about the tax code.

Relatively few taxpayers pay an enormous percentage of the total federal income tax, and most of them are people who work for a living and have adjusted gross incomes of $100,000 to $500,000, which is the sweet spot for tax revenue. They account for 20.2 percent of total returns but pay a whopping 44.9 percent of total tax. The average tax rate for this group ranges from 11.9 percent for those with less than $200,000 in adjusted gross income to 19.6 percent for those with $200,000 to $500,000. Above those income levels, the rate rises to close to 25 percent and then declines to 22.6 percent for taxpayers earning more than $10 million.