Everyone is entitled to his own opinion, as a senator once famously said, but not his own facts.

In Washington, D.C., every politician, lobbyist, activist, taxi driver and barber has an opinion. But only a few institutions are trusted with the facts.

On spending, one is the Congressional Budget Office .

Known around the nation's capital as the CBO, the federal agency is in charge of telling Congress how much its legislation will cost taxpayers. But it is required by law to avoid making any policy recommendations in its reports.

That makes it something of a scorekeeper in the ongoing debate over spending in the federal budget. In fact, the process for determining how much a bill will cost is known as "scoring."

On Sept. 16, the CBO made news when it scored the first version of the heath-care reform proposal released by the Senate Finance Committee.

Democrats and Republicans don't agree on much about the reform, but they agreed the agency's numbers were at the heart of the fight.

In a floor speech, Republican Sen. Lamar Alexander of Tennessee cited a letter from the CBO that estimated the 10-year cost of expanding coverage would be more than $1 trillion.

"All of the health care reform bills produced so far by the Democratic Congress ... flunk the first test, which is reducing cost — cost to the American people and cost to the American government," he said.

Across the aisle, Democratic Sen. Roland Burris of Illinois made the exact opposite argument — that a new health care system would help the economy — using figures from the same agency.

"Critics have said a public plan will cost too much ... but the nonpartisan Congressional Budget Office conducted a study that tells a very different story," he argued.