[US midterm election] Opinion poll predicted a blue wave, but did not see a tsunami

Ahead of the U.S. midterm elections, public opinion polls accurately predicted a 'blue wave' (Democratic Party victory), but failed to properly capture its power.

This is an assessment released by the U.S. online media Axios on the public opinion polls conducted ahead of the elections on the 4th (local time), the day after the midterm elections.

According to the average opinion poll calculated by the election forecasting agency Silver Bulletin, the Democratic Party was expected to win by 8.9 percentage points (p) in total votes in the House of Representatives, but in reality, it achieved a landslide victory by a margin of 13 percentage points.

This means that although public opinion polls predicted a blue wave, they did not foresee a ‘blue tsunami’ (Democratic Party landslide victory).

In fact, pollsters have had a hard time accurately predicting the voting trends of Republican voters since the advent of President Donald Trump.

Due to ‘Shy Trump’s reluctance to publicly express support for President Trump, President Trump’s approval rating was undersampled for three consecutive presidential elections in 2016, 2020, and 2024.

According to Silver Bulletin analysis, the Democratic Party's vote share was overestimated by 3 percentage points in 2016, 4.7 percentage points in 2020, and 2.9 percentage points in 2024.

In 2018 and 2022, when the midterm elections were held, the error was relatively small, within 1%p.

However, in this midterm election, opinion polls were conducted in a way that underestimated the Democratic Party's vote share by an average of 4 percentage points.

Some point out that improving the survey method to prevent undersampling of Republican supporters may have led to the side effect of undersampling Democrats.

Not all predictions from public opinion polls are wrong. In the case of Atlas Intel, it predicted that the Democratic Party's vote rate would be high with a difference of 14.1% points, giving a figure that was relatively close to the reality.

The New York Times (NYT) also predicted 11%p and was not far off. Well-known organizations such as YouGov and Ipsos predicted differences of 9%p and 8%p, respectively.

The NYT estimated that the Democratic Party would win the House of Representatives election in this midterm election with a 13% point margin of vote and reported, “This is the biggest victory achieved by any one party (in the United States) in 50 years.”

During the 1974 midterm elections and 1976 presidential election, when the Republican Party was on the defensive due to the Watergate incident, the Democratic Party won a landslide victory, widening the gap in the House of Representatives vote percentage by 16.6% points and 14.1% points. This 13% point difference is comparable to the time of the Watergate incident.