Warren Buffett’s claims that tax rates won’t affect investment decisions among wealthy Americans is just wrong, said Clifford Asness, managing and founding principal of AQR Capital Management.

Buffett, a champion of President Barack Obama’s proposals to hike taxes on top U.S. earners, wrote in a New York Times column recently that tax rates don’t affect investment decisions.

Math says otherwise, Asness wrote in a Wall Street Journal OpEd, pointing out that everyone who pays taxes uses after-tax cash flows when calculating whether or not an investment will generate profits.

Editor's Note: How You Lost $85,000 During the Last Decade. See the Numbers.

“Somewhere in the spreadsheet there is a number, say 20 percent or 28 percent or a Gallic 75 percent, representing the taxes you’ll pay on the assumed cash flow — and you only count the amount you’ll get after paying this tax,” Asness wrote.

“If you turn the tax rate up high enough, projects or companies that looked like good investments become much less attractive and vice versa.”

While Buffett is correct in his argument that top U.S. earners will continue to invest even if taxes go up, investing behavior will change.

“Fewer and smaller investments will be made if the after-tax prospects are worse. It’s just math and logic, unassailable and commonly accepted regardless of one’s political persuasion,” he wrote.

“Taxes matter. They matter to business and life decisions alike. They matter to the rich and to the poor. They are, or at least they should be, incorporated into nearly every financial decision made,” Asness added.

“Discussing tax policy without acknowledging this fundamental reality is bizarre. Actually asserting the opposite is willful ignorance.”

President Barack Obama and House Speaker John Boehner, R-Ohio, continue to negotiate the role tax hikes must play as part of broader fiscal reforms needed to craft a 2013 spending framework.

At the end of this year, tax breaks are scheduled to expire at the same time automatic cuts to government spending are due to kick in, a combination known as a fiscal cliff that could send the country into a recession next year if left unchecked by Congress.

The White House has said those bringing in over $250,000 a year should pay more in taxes, with Republicans reportedly countering that the threshold should be closer to $1 million.

While a deal still remains far off, Washington observers say progress is under way since Republicans now appear to be warming up to tax hikes.

“Boehner has now accepted the premise of higher rates. So now we’re just arguing over details,” said Greg Valliere, chief political strategist at Potomac Research Group, according to Reuters.

“I think it’s a significant step.”

Editor's Note: How You Lost $85,000 During the Last Decade. See the Numbers.