With less than one week remaining until Election Day, Democrat Kamala Harris and Republican Donald Trump are in a tight race to win over undecided voters.

According to the polls, few United States presidential elections have been as tightly contested as this one.

Harris and Trump are in a dead heat and the outcome could be decided by voter turnout in the seven key swing states.

Who is in the lead?

As of Tuesday, FiveThirtyEight’s daily election poll tracker shows Vice President Harris leading the national polls with a 1.5-percentage-point advantage over former President Trump. However, this lead has decreased slightly from last week’s 1.8-point margin, indicating that Trump is gradually closing the gap.

According to the latest Reuters/Ipsos polls, Harris’s lead over Trump has narrowed in the election’s final stretch.

Harris holds a narrow lead of just one percentage point over the Republicans, 44 percent to 43 percent, nationally, according to the poll. The poll has a margin of error of approximately three percentage points in either direction.

When asked which candidate had a superior approach to the economy, unemployment and jobs, voters in the poll favoured Trump by 47 percent to 37 percent. Trump has also maintained an advantage on economic and immigration issues.

The poll also showed that Harris’s lead on the issue of political extremism is diminishing. Approximately 40 percent of voters felt she had a better approach to addressing political extremism and threats to democracy, while 38 percent favoured Trump.

Both candidates’ margins are within the average of the polls’ margins of error, meaning that either could potentially be in the lead. While most polls indicate Harris is ahead in the national vote, the two candidates are closely matched in swing states.

It’s important to note that while national surveys offer insights into voter sentiment, the Electoral College will ultimately determine the winner, not the nationwide popular vote. Many states tend to strongly favour either Republicans or Democrats.

What are the polls saying about the swing states?

The seven key swing states are Pennsylvania (19 electoral votes), North Carolina (16), Georgia (16), Michigan (15), Arizona (11), Wisconsin (10), and Nevada (6), which together hold 93 Electoral College votes.

According to FiveThirtyEight’s average of recent surveys, Harris and Trump are within the margin of error in each of these states. In Michigan, Harris maintains a slight lead over Trump, with a margin of +0.8 points since last week. She has also gained a narrow advantage in Nevada and Wisconsin, highlighting how easily these states could swing in either direction.

Conversely, Trump has a slight edge in Pennsylvania and a more significant lead in North Carolina, Arizona and Georgia.

Continuing last week’s trend, if the narrow margins reflected in the poll averages hold on election night, Trump is favoured to win. However, even a small shift away from him in these critical states – or an underestimation of Harris’s support – could result in a victory for the vice president.

Notably, in the 2020 presidential election, Georgia, where Trump is currently leading, shifted from Republican to Democratic after nearly 30 years of voting Republican. Similarly, Arizona, where Trump also has a lead, was won by Democrats by just 0.3 percentage points.

How trustworthy are polls?

Election polls predict how the population might vote by surveying a sample of voters. Surveys are most commonly conducted by phone or online. In some cases, it is via post or in person.

Poll trackers, which aggregate a number of polls together, are weighted based on a number of factors, such as the sample size of the poll, the pollster quality, how recently the poll was conducted and the particular methodologies employed.

Polls are never 100 percent accurate. Both the 2016 and 2020 US elections saw opinion polls underestimate the popularity of Republican candidates.

Pollsters got it wrong again in the 2022 midterm elections. That time, they undercounted the support for Democrats and predicted a win for Republicans, only to be proven wrong.

Experts note that while pollster services are sophisticated, they have a limited shelf life.

“The problem is that, as the cliche goes, they’re snapshots in time, so as soon as you see them, they’re already out of date. The big question [this year is] with the undecided voters,” Steven Erlanger, the European diplomatic correspondent at The New York Times, told Al Jazeera’s Inside Story programme.

Many of the polls conducted before this year’s presidential election have shown the difference in support between Harris and Trump within the margin of error.