Further polling since the Republican National Convention has tended to confirm our impressions from earlier this week: Donald Trump has almost certainly gotten a convention bounce, and has moved into an extremely close race with Hillary Clinton. But Trump’s convention bounce is not all that large. You can find polls showing almost no bounce for Trump, and others showing gains in the mid-to-high single digits. Those disagreements are pretty normal and, overall, the polls suggest a net gain of 3 to 4 percentage points for Trump. That would be right in line with the average bounce in conventions since 2004, although it is toward the small side by historical standards.
Trump’s position in our polls-plus forecast, which adjusts for convention bounces, is almost unchanged over the past week; the model continues to give him about a 40 percent chance of winning the election, meaning that Clinton has a 60 percent chance.
Without adjusting for the convention bounce, however, the election is a dead heat. Our polls-only forecast, which doesn’t account for the convention bounce, gives Clinton just a 53 percent chance of winning, and our now-cast — which is more aggressive than the polls-only forecast and estimates what would happen in a hypothetical election held today — has Trump as a 55 percent favorite.
But I want to focus on some relatively technical subject matter today, apart from Trump’s convention bounce. FiveThirtyEight’s isn’t the only election forecast out there. Most of the others give Clinton a better chance than we do – some of them give her as high as an 80 percent chance, in fact, despite her recent slide in the polling. Why are our models more pessimistic about Clinton’s …