How AP calls elections before all the votes are in

Stickers are given to voters Tuesday, June 5, 2012, in Milwaukee. Wisconsin Republican Gov. Scott Walker is taking on Democratic challenger Tom Barrett in a recall election. (AP Photo/Jeffrey Phelps)

The call came at 10:05 p.m. EDT Tuesday, just over an hour after polls closed in Wisconsin: Republican Wisconsin Gov. Scott Walker survived the recall election and defeated Democrat Tom Barrett.

And that's when the questions started coming in: How can an election be called before all the votes are counted? And how can an organization call a race if people are still waiting to vote?

AP makes its calls based on a variety of factors, and never calls a race before poll close, says David Pace, a news editor in Washington who coordinates AP election calls.

If people were still voting when the call was made, they had to have been in line by the time polls closed, he said. No one new is allowed to get in line once polls close.

The AP calls races based on early vote returns provided by state and county elections offices, exit polls that conducted with voters and vote results from a random sample of precincts around the state. It's a complicated process that also compares the voting history of counties to make sure results are in line with past trends.

Our call in the Wisconsin governor's recall election was made with 37 percent of precincts reporting. Tabulations of early returns showed Walker ahead 59 percent to Barrett's 40 percent.

Although less than half of the state's precincts were reporting, only a handful of counties hadn't reported some of their results. So voters all across the state were represented in the calculations.

Also, most of the big counties had reported some of their votes. Milwaukee County, the state's largest and home to Barrett, had reported the fewest votes of the big counties. But the AP could still make the call because of the size of Walker's lead, Pace said.

"We knew Milwaukee was going to come in much more heavily for Barrett, but with such a big lead built-up statewide for Walker, there weren't enough votes for Barrett to overcome it," he said.