Zeynep Tufekci writes:

For weather, we have fundamentals — advanced science on how atmospheric dynamics work — and years of detailed, day-by-day, even hour-by-hour data from a vast number of observation stations. For elections, we simply do not have anything near that kind of knowledge or data. While we have some theories on what influences voters, we have no fine-grained understanding of why people vote the way they do, and what polling data we have is relatively sparse.

Consequently, most electoral forecasts that are updated daily — like those from FiveThirtyEight or The Economist — rely heavily on current polls and those of past elections, but also allow fundamentals to have some influence. Since many models use polls from the beginning of the modern primary era in 1972, there are a mere 12 examples of past presidential elections with dependable polling data. That means there are only 12 chances to test assumptions and outcomes, though it’s unclear what in practice that would involve.

A thornier problem is that unlike weather events, presidential elections are not genuine “repeat” events. Facebook didn’t play a major role in elections until probably 2012. Twitter, without which Mr. Trump thinks he might not have won, wasn’t even founded until 2006. How much does an election in 1972, conducted when a few broadcast channels dominated the public sphere, tell us about what might happen in 2020?

Interpreting electoral forecasts correctly is yet another challenge. If a candidate wins an election with 53 percent of the vote, that would be a decisive victory. If a probability model gives a candidate a 53 percent chance of winning, that means that if we ran simulations of the election 100 times, that candidate would win 53 times and the opponent 47 times — almost equal odds.

In its final forecast in 2016, FiveThirtyEight gave Hillary Clinton a 71.4 percent chance of victory. (The digit after the decimal providing an aura of faux precision, as if we could distinguish 71.4 percent from 71.5 percent.) All that figure really said was that Mrs. Clinton had a roughly one-in-three chance of losing, something that did not get across to most people who saw a big number. Most sites gave an even bigger number, with The New York Times predicting Mrs. Clinton had an 85 percent chance of winning on the day of the vote.

Since 2016, sites like FiveThirtyEight have gotten much better at presentation, focusing on odds and scenarios, and even explicitly urging people to remember that upset wins are possible. Still, the point of a forecast is to predict, and people may not be that likely to think “anything can happen” when they see what appear to be overwhelming odds in one direction. [Continue reading…]