How do news outlets decide when to "call" an election?

With Biden winning the Michigan primary yesterday, I’ve been seeing complaints on social media from Bernie Sanders supporters complaining that MSNBC called the election for Biden while there were still people at some polling places waiting in line to vote. They’re claiming that by calling the election when they did MSNBC influenced the result.

I think that’s… unlikely, to put it nicely. I think that by they time they called it, it was mathematically impossible (or at least so improbable that for all intents and purposes the same as impossible) for those remaining voters to actually change the outcome, even if 100% of them were planning on voting for Sanders (which itself would be extremely improbable).

But how do they decide when to call it, exactly? Is there some mathematical formula that they use? Is that formula published, of something that they consider proprietary?

If they called an election before the polls were closed that sounds like exit polls.

From how I understand it, it was called after the time when the polls officially closed, but since people who were in line before closing time are still allowed to vote, some people at a few polling places with long lines still hadn’t voted yet.

AFAIK, networks have pledged to not call any races until the polls close, even if the winner is obvious. IIRC, it dates back to 1972, when they were calling states for Nixon before the polls closed in the west. The complaint was it would depress voter turnout in non-presidential races, so they voluntarily decided to hold off even if they knew the result.

Note that most states allow people to vote if they’re on line before the deadline. So there will be some votes cast after they call it, but those aren’t considered a problem.

They’re also holding off longer on close races after 2000 Florida debacle.

Regarding people still in line, that’s not a big of an issue for the Democratic Primary. The contests are not winner-take-all, so the margins matter.

In the 2012 election, the head of the RNC (whose name I have forgotten) just about blew a gasket when Fox of all people called Ohio for Obama at a time in the evening when Romney still had a lead in the already tallied votes. They were right of course.

I do not know the details, but it is going to go roughly like this: The precincts already counted were 50.1% for Romney, but were 50.9% for McCain four years earlier, so we assume the Republican vote is falling off by .8%. The precincts not yet counted were 51.3% for Obama 4 years ago so we assume they will go by 52.1% for Obama this time. Add it up and Obama will have at least 51% of the vote. This ignores minor parties of course.

With all the data they have now, they could possibly do a finer-grained analysis. Maybe estimate the votes of blacks, of suburban women, of urban men, that sort of thing. I don’t know how much state-by-state data they have and whether they use it.

Part of that debacle was that Florida got called for Gore before all of Florida had finished voting. It’s easy to forget that parts of the panhandle are in the Central time zone.

That was Karl Rove. Here’s a video of him bitching that Ohio had been called. Includes the camera following Megyn Kelly walking down the hallway to interview the Fox News statisticians who made the call.

There is this article, among others that goes into the theory that the Anonymous group stopped Rove from stealing the Ohio election, just as he had in 2004. Interesting read, though little can be substantiated.

Nitpick: I believe it was 1980, when NBC called the race for Reagan at 8:15 Eastern time (5:15 on the west coast) and Carter conceded at 9:50 (6:50) when polls were still open for another hour. People argued about the effect of downballot races. The GOP picked up senate seats in Washington and Alaska, part of a 12-seat pickup that flipped the senate for the first time in 26 years.