What happened to the convention boost?

This week, the odds on Polymarket, a cryptocurrency betting platform, shifted in favor of Donald Trump’s presidential bid, even while Kamala Harris and Tim Walz were highlighted at the Democratic National Convention in Chicago.

Trump’s chances of winning dropped significantly during the Republican National Convention in Milwaukee, going from 71% at its peak following the assassination attempt to 63% the day after the convention ended.

As of Friday at 1 p.m. EDT, betters appear less confident in Trump compared to earlier in the week, with the betting odds suggesting he has a 49% chance of winning, and Harris a 48% chance. Before the convention, betters had Harris’ winning odds reaching as high as 54%.

Predictions for the 2024 presidential election

Harry Crane, a statistics professor at Rutgers University, has examined election results since 2016, examining them alongside predictions from polls and betting markets like Polymarket.

During the week of the Democratic convention, polling data from Real Clear Politics indicated that Harris’ national average was on the rise, while Trump’s numbers slightly declined. The bettors on Polymarket and Betfair, the largest online betting exchange in the world, demonstrated opposing trends.

Why is Kamala Harris’ betting odds declining while polls are increasing?

So what insights can we gather from the bettors? “The market price at any specific moment reflects the collective sentiment of the market based on the information available,” Crane noted and offered some thoughts on what bettors might be considering:

◾ Evaluation of Harris’ plans: After Harris revealed her economic strategy on August 16, bettors may anticipate possible objections from voters in key demographics. “Participants in these markets engage in thorough analysis,” Crane expressed. “They could be well aware of state demographics, such as those in Pennsylvania, down to the specifics that could sway the election.”

◾ Recent polling outcomes: Although Harris’ campaign sees slight progress in overall polls, Trump has shown 2 percentage points higher in the latest survey conducted in Arizona, a crucial state for the election.

◾ Robert F. Kennedy Jr.: There has been ongoing speculation about the direction of Kennedy’s campaign. He is scheduled for a press conference today, leading to rumors that he may withdraw from the race and support Trump.

Crane suggested that similar speculation about Trump’s potential rivals likely impacted his odds negatively during the Republican convention. He indicated that bettors might view Harris as a more competitive Democratic candidate, leading to a dip in Trump’s winning probabilities amid speculations that Joe Biden could exit the race.

Is there a boost post-convention?

Crane posited that bettors may expect a boost in poll numbers following the conventions and thus factor that into their analyses, suggesting that overall election boosts have become less common.

From the start of the conventions to the following week, it appears that neither Trump nor Harris will experience significant increases in national polling tracked by Real Clear Politics.

Presidential candidates’ polling improvements after conventions

Research from The American Presidency Project reveals that since 1964, candidates typically experience around a 5 percentage-point increase in polling due to conventions, although this hasn’t occurred since 2008 when John McCain and Barack Obama saw increases of 6 and 4 points, respectively.

Next up: What odds will bettors give to Trump’s and Harris’ campaigns following their initial debate scheduled for September 10.

Have election odds historically been accurate in presidential races?

Since 1866, the favored candidate in betting markets has lost only twice, as reported by the Conversation, a nonprofit news outlet.

The two notable upsets were in 1948 when Democrat Harry Truman defied eight-to-one odds to win against Republican Thomas Dewey, and in 2016 when Trump surpassed seven-to-two odds to defeat Hillary Clinton.