Credit Zell Miller for PolitiFact's existence.

PolitiFact founder and editor Bill Adair says it was the former Georgia senator's speech at the 2004 Republican National Convention in New York that gave him the idea to create the online fact-checking site that has already won a Pulitzer Prize and spread to five states.

“Zell Miller made a speech and he attacked Sen. John Kerry for supposedly wanting to cut defense and claimed Kerry wanted to oppose a lot of defense proposals,” Adair recalls. “Miller's speech was reported with little real scrutiny. After that campaign, I felt like the media had let voters down. We had not held candidates and elected officials accountable. I felt it was time to do more aggressive fact-finding.”

Adair, also D.C. bureau chief for the St. Petersburg Times, approached his bosses at the paper and plans began for the site, which launched Aug. 22, 2007.

“It is not a blog, it is truly a web form of journalism,” Adair says.

And as PolitiFact approaches its third anniversary on Sunday, the site has become the standard for neutral fact-checking outlets. Created with only two full-time staffers and one site, the franchise has expanded to local versions in Texas, Florida, Georgia, Rhode Island and Ohio. Adair's crew is now at five, with three of them in Washington, D.C.

“From the start, I believed the Truth-O-Meter was as valuable at the state and local level as at the national level,” Adair said.

PolitiFact fans, and foes, know the Truth-O-Meter is at the heart of the website's mission. Simply, it takes comments by public officials -- and more recently media pundits -- and examines the facts of their statements. Each is rated for its amount of truth with ratings that include: true, mostly true, half true, mostly false, false and “Pants on Fire.”

Adair admits choosing which statements to fact-check is subjective, but says no political views or ideological leanings are involved. Those on the right and left get equal scrutiny.

“Our number one criteria is whether somebody would be curious if it is true,” he says. “Our goal is to serve readers' curiosity.”

Each Truth-O-Meter rating is reviewed by at least three PolitiFact editors before it is posted: “Most of the time they agree with the reporter. We are a neutral news organization, we are focused on checking facts, not on any particular side in the political discourse.”

Last weeks' Truth-O-Meter subjects ranged from Rachel Maddow to John McCain.

“It is an editorial decision like any decision of what to cover for a news outlet,” Adair says. “But we make it based on what topic readers would mostly be interested in. We are not fact-checking opinions, we are fact-checking claims.”

ABC News thought enough of PolitiFact to sign the site up to do weekly reviews of This Week.

PolitiFact is not without its critics, some who claim its fact-checking, on the right and left, is slanted to help one side or another.

Arianna Huffington wrote a critique of PolitiFact when it put her to the truth test in July, and gave her a half-truth rating for a This Week appearance:

As long as we allow truth backed up by a mountain of evidence to be, in the name of "pious fairness," downgraded to Half True, that's the way the planet we're all living on is going to continue to operate. And that's a fact.

But it also has its fans, such as the Columbia Journalism Review, which declared in a July 12 story:

PolitiFact might be pedantic at times, but only by necessity. If our pols and pundits insist on lowering the public discourse to sound bite slings and arrows, we need an aggressive, attentive press to draw conclusions about what should stick and what should bounce.

Sarah Palin, meanwhile, had one of the most reported skirmishes with PolitiFact, shooting back earlier this month when the site gave her a “Pants-on-Fire” rating for stating Obama was pushing the largest tax increase in U.S. history.

“It's a tax increase of $3.8 trillion over the next 10 years, and it will have an effect on every single American who pays an income tax,” Palin said in a Fox News Sunday appearance at the time.

After PolitiFact corrected her and gave her the worst rating, she shot back on Facebook, declaring:

Yesterday, PolitiFact.com fact-checked my statement about the coming $3.8 trillion Obama tax hike - the largest tax increase in history. They did such a bad job of it, however, that I feel compelled to fact-check the fact-checkers.

First of all, they claim that there are Democrat proposals which would “keep the tax cuts for individuals who make less than $200,000 and couples who make less than $250,000.”

Unfortunately for PolitiFact, no such proposal exists. They admit as much, by the way, when they state that “There are no formal congressional proposals yet to keep the Bush tax cuts in place, so we don't have precise estimates from official sources like the nonpartisan Congressional Budget Office." That doesn't stop them, though, from claiming I “confuse the issue” by “using numbers that assume all the tax cuts are going away. That is not the Democratic plan nor is it President Obama's plan.”

Adair says PolitiFact also has its own correction issues, but says they are few. Out of some 1,600 Truth-O-Meters posted in the past three years, he contends only “several dozen corrections” have been needed. But he said he does not keep track of them.

“Those numbers reflect the tremendous care we put into this,” he said of the focus on correct facts.

PolitiFact marked a milestone for all websites when it won the 2009 Pulitzer Prize for National Reporting.

In its announcement, the Pulitzer Board declared the website during the 2008 election succeeded in “separating rhetoric from truth to enlighten voters.”

Adair added fact-checking of media pundits and reporters in March 2009: “We came to the realization that the political discourse is also coming from pundits and talk show hosts.”

There is also the Obamameter, created in April 2009 to monitor the president's campaign promises.

Adair says he hopes to eventually have a PolitiFact site for each state. “That's my goal,” he told me. “Every candidate and elected official in America ought to face the Truth-O-Meter.”