Projecting Confidence

I didn’t think you needed me.’ I don’t know how we’ll ever calculate how many people thought it was in the bag, because the percentages kept being thrown at people — ‘Oh, she has an 88 percent chance to win!’Is it plausible that forecasting could have affected the election?For this to affect the election, it has to be out there in the media reaching potential voters, depress turnout, and to affect Clinton supporters (and/or Clinton campaigners) moreso than for Trump.In 2016 there was significantly more media covrerage of probablistic forecasts than in past election cycles:(Number of articles mentioning probabilistic forecasts indexed by Google News.)And our research (see results below) suggests that candidate who is ahead in the polls is more affected by probablistic forecasts..In 2016, that was Hillary.But irrespective of 2016, when you look at who engages with this material in both social media and television media, it’s outlets with a left-leaning audience..The websites that present their poll aggregation results in terms of probabilities have left-leaning (negative) social media audiences — only realclearpolitics.com, which doesn’t emphasize win-probabilities, has a conservative audience:These data come from the average self-reported ideology of people who share links to various sites hosting poll-aggregators on Facebook, data that come from this paper’s replication materials.When you look at the balance of coverage of probabilistic forecasts on major television broadcasts, there is more coverage on MSNBC, which has a more liberal audience.How much influence do forecasters really have?Well, FiveThirtyEight’s 2018 coverage seems to have been highly influential..After their real-time forecast had GOP’s odds of taking the House spiking at 60% at around 8:15PM, PredictIt’s odds on the GOP rose above 50–50, & U.S..government bond yields saw brief spike of 2–4 basis points.This spike seems to have occurred because a number of big, Republican-dominated districts started reporting returns before those that went toward Democrats and because it was making inferences from partial vote counts:This was first reported by Colby Smith & Brian Greeley of FT.com..They report that because markets expected to see more inflation under a Republican House (high spending, low taxes) the U.S..Bond yield rose.Was this just a correlation?.Possibly, but there was pretty much nothing else happening in the U.S., and it was like 1 am in Europe, as pointed out in the FT.com piece above.Josh Tucker suggested that 538 might be driving prediction markets back in 2012 in a Monkey Cage blogpost.Our research on forecasting and perceptionOur research shows that probablistic election forecasts make a race look less competitive..Participants in a national probability survey-experiment were substantially more certain that one candidate would win a hypothetical race after seeing a probablistic forecast than after seeing the equivalent vote share estimate and margin of error..This is a big effect — those are confidence intervals not standard errors, with p-values below .Why do people do this?More research is needed here but we do have some leads..First, small differences in the election metric most familiar to the public — vote share estimates — generally correspond to very large differences in the probability of a candidate’s chance of victory.Andy Gelman referenced this in passing in a 2012 blogpost questioning the decimal precision (0.1 percent) that 538 used to communicate its forecast on its website:That’s right: a change in 0.1 of win probability corresponds to a 0.004 percentage point share of the two-party vote..I can’t see that it can possibly make sense to imagine an election forecast with that level of precision…Second, people sometimes confuse probabilistic forecasts with vote share projections, and incorrectly conclude that a candidate is projected to say win 85% percent of the vote, rather than to having an 85% chance of winning the election.. More details

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