The US election campaign is entering its final weeks and voters will go to the polls on November 5 to choose the next president.

Early voting is already underway in a number of states, including battleground states like North Carolina and Georgia.

With less than three weeks to go until the election, Democratic Vice President Kamala Harris and Republican former President Donald Trump are battling to sway undecided voters.

However, the popular vote does not determine the winner. Instead, it determines which electors will represent each state in the Electoral College, which does choose the president.

To win, a candidate must secure 270 of the 538 electoral votes up for grabs. The Electoral College votes are distributed among the states based on their relative populations.

Who is leading the way?

According to FiveThirtyEight’s daily election tracker, Harris is currently leading in national polls and has a 2.4 percentage point lead over Trump.

In July, President Joe Biden, a Democrat, dropped out of the presidential race and endorsed Harris as his replacement. Since then, the vice president’s ratings have risen from lower numbers under Biden.

But the race is still exciting. FiveThirtyEight’s election forecast suggests Harris is favored to win 54 times out of 100, while Trump wins 46 times out of 100.

Which states could influence the presidential election?

Swing states, also called battleground states, can influence the outcome of national elections.

One of the defining characteristics of a swing state is its ambiguous political preferences, with no party having overwhelming support.

This year, the states of Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin are being closely watched.

In the 2020 presidential election, Georgia switched from Republican red to Democratic blue after nearly three decades of voting Republican, and in Arizona, Democrats won by a narrow margin of 0.3 percentage points.

Polls show Trump and Harris in a close race in swing states. Polls in these states are more important in determining the winner than national polls because the Electoral College, not the popular vote, chooses the president.

What happens if Harris and Trump end in a tie?

There are a total of 538 electoral votes. To win the election, a candidate must reach 270.

Given the nature of how electoral votes are distributed, specific combinations of states could result in a tie of 269 votes. Such a scenario is possible, but not likely.

If no candidate receives at least 270 electoral votes, a contingent election will take place with the U.S. House of Representatives determining the winner.

Each state’s delegation in the House would cast one vote, and a candidate must receive a majority (26 out of 50) of the state delegation’s votes to win.

The U.S. Senate would then elect the vice president, with each senator casting one vote and a simple majority (51 votes) required to win.

How do polls work?

Election polls predict how the population might vote by surveying a sample of voters. Surveys are usually conducted by telephone or online. In some cases this is done by post or in person.

Survey trackers, which aggregate a number of polls, are weighted based on a number of factors, such as the sample size of the poll, the quality of the poll, how recently the poll was conducted, and the specific methodologies used.

How accurate are polls?

Opinion polls are never 100 percent accurate. In both the 2016 and 2020 US elections, opinion polls underestimated the popularity of Republican candidates. Despite polls for the 2022 midterm elections becoming more accurate, many still remain skeptical about the election results.

Part of the reason for the inaccuracy in the polls in recent years relates to the ability to reach voters. Opinion polls are often conducted via telephone surveys; however, fewer people are likely to answer calls. Non-response bias is another reason for inaccuracy – for example, in recent years, Trump voters have chosen not to respond to polls. Additionally, changes in turnout have affected the accuracy of polls. In 2020, for example, turnout was much higher than expected.

There is a mathematical margin of error in polls because they use small, select groups of people to determine the choices of a larger population. That margin of error in American polls indicates the range within which the actual result is likely to fall. With a sample size of 1,000 people, the margin of error is about plus or minus 3 percent.

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.