Late-Stage Surges: Understanding Shifts in Polling Data Before Elections

The Henry Jackson Society

As the election day nears, polling data often shows significant shifts. This phenomenon can be attributed to several factors and understanding these elements provides valuable insights into the actions of political parties and communications strategies around political campaigns.

Polling Can Become More Accurate

Polling accuracy tends to improve closer to the day of the election because voters’ preferences solidify and late-campaign events have a more immediate impact. Early polls reflect the fundamental political and economic conditions, but as the election approaches, they increasingly capture the evolving voter sentiment and campaign dynamics. The mean absolute error of polls decreases significantly, from around 4.0 percentage points 200 days out to about 2.0 points just before the election, indicating a closer alignment with the actual vote outcome as election day nears.

This suggests voters tend to pay more attention to the election as the voting day approaches, leading to shifts in opinion influenced by late-breaking news or campaign events. A notable example is the 2017 UK General Election, where Labour, led by Jeremy Corbyn, saw a significant surge in the final weeks.

Initially trailing significantly behind the Conservatives, Labour managed to narrow the gap considerably. This shift was attributed in part to Corbyn’s performances, but also to the then Prime Minister Theresa May’s disastrous ‘Dementia Tax’.

Intensified Campaign Efforts

Campaigns often ramp up their efforts in the final weeks, including targeted advertisements, rallies, and grassroots mobilisation, aiming to influence undecided voters. The 2019 UK General Election is a prime example. The Conservative Party, under Boris Johnson, intensified their focus on the “Get Brexit Done” message. This clear, resonant message, amplified through extensive media and ground campaigns, successfully swayed many undecided voters and reinforced the support of those leaning towards the Conservatives, leading to a decisive victory.

Media Coverage

Media coverage also intensifies, bringing more attention to the candidates and their platforms. This was evident in the 2016 US Presidential Election.

The final weeks saw a media frenzy over various controversies and breaking news, such as the FBI’s announcement about reopening the investigation into Hillary Clinton’s emails. These high-intensity media cycles can greatly influence voter perceptions and decisions, contributing to the volatility observed in the polls.

Intriguingly, we can see, as observed earlier, a significant shift in polling as we approached this election. However, what is interesting in this case is that the polls moved in Hilary Clinton’s favour despite the fact in was Donald Trump who ultimately won the Presidency.

Strategic Voting Considerations

As the election day gets closer and the stakes get higher some voters switch to strategic voting. They switch to supporting a candidate they perceive as having the best chance to win against an undesired opponent.

For example, voters in Southern England might switch their support from Labour to the Liberal Democrats if they believe it could prevent a Conservative win. The Electoral Reform Committee estimate that 32% of voters in 2019 General Election voted for parties that were not their first preference for this reason. This strategic shift can cause noticeable changes in polling data as voters align their choices with broader electoral strategies.

Recognising these dynamics can help explain the often unpredictable nature of election outcomes and the crucial importance of the final push in any campaign.

As voters become more focused and campaigns deploy their most potent strategies, the electoral landscape can change rapidly, making the last days before the election some of the most impactful.


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