Condensed from Vox (read full article here):
“For decades now, news agencies … have been projecting presidential election winners … before all the votes are in. It’s an important service that greatly speeds up our knowledge of who’s won … without having to wait for the final tally from state authorities …. Their track record for accuracy has been excellent, but in the rare cases it goes wrong, it can go very wrong …. This year could be especially tricky for election callers because of the unprecedented number of mail-in/absentee ballots ….
“The news outlets … emphasize that the ‘decision desks’ … are staffed by professionals, often PhDs in political science or related fields, who are well-insulated from the more opinionated sides of their news operations. For instance, Arnon Mishkin, Fox News’s decision desk leader, is known as a straight shooter by observers across the political spectrum, not beholden to the right-wing figures at his network. … The decision desks at other networks are similarly professionally staffed ….
“Arguably the most famous, and perhaps the most labor-intensive, election-calling operation is run by the Associated Press. … [I]t will employ more than 4,000 stringers (freelance reporters hired for this assignment specifically) and send them to county election centers, where they’ll call in raw vote totals to AP’s decision desk as they come in. Some 800 vote-entry clerks will screen the data for abnormalities and then enter them into software that also raises flags if the numbers look ‘inconsistent or statistically unlikely.’
“’AP’s race callers are staff who are deeply familiar with the states where they declare winners. Most have called races in a state for many years,’ the agency explains. The calls they make depend heavily on incoming vote totals being reported from counties, analyzed in conjunction with knowledge of how those counties typically vote, their demographics compared to those of the state as a whole, etc. …
“The AP has moved away from exit polling in favor of … an alternative method that accounts for the large chunk of voters who vote before election day, either in early voting or via absentee/mail. Either way, exit polls [or AP’s method] can make it possible to call easy, not-close races early. …
“The unusually high level of absentee voting/vote-by-mail in 2020, amid the Covid-19 pandemic, could complicate calling efforts. To get a sense of what the vote that’s in at, say, 8:30 pm means, you have to have a sense of how many people voted in person that day versus by mail, how much of the initial vote total is by mail versus in person, where the in-person votes come from, how in-person versus by-mail voters lean in key races, and so forth. With voting methods changing dramatically this year, that all could be harder to predict. … The result might be more cautious network calls this year than in the past. …
“The key … is patience. Part of being a good race caller is declining to call races when there’s legitimate uncertainty. That means you might not get definitive answers as soon as you want to on election night, or even election week. Be patient, and we’ll all figure this out together.”
Actually all this is actually all about nothing. The race should only be called once the electors cast their votes in the electoral collage. That is what all the networks should be reporting on, as that determines who the President and Vice President will be. All the networks do a fine job of ignoring it, except for the local networks in state capitals who feel some civic duty to report on why all these people descended on the Capital possible in foul weather to participate in this institution. Some reporters may think there are actual classes being offered at the state capital for new legislators.
A presidential election isn’t “nothing.” Given the First Amendment, the press can report it however they like. And you are right, there are classes for new legislators. See, e.g., https://donahue.umass.edu/special-projects/academy-for-new-legislators