Opinion Polls, Predictions, and Their Limitations

This lesson examines the role of opinion polls in UK elections — how they work, their influence, and their significant limitations.

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What Are Opinion Polls?

Opinion polls are surveys designed to measure public opinion on political issues, party support, and leader approval. They are conducted by polling companies using samples of the population.

Key UK Polling Companies

Company	Method
YouGov	Online panel surveys; large sample sizes
Ipsos	Telephone and online interviews
Survation	Online and telephone; known for accurate 2017 exit-day poll
Savanta ComRes	Online and telephone surveys
Opinium	Online panels
Deltapoll	Online panels

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How Polls Work

1. Sampling: A representative sample of the population is selected (typically 1,000–2,000 people)
2. Questioning: Respondents are asked about voting intention, leader approval, issue salience, etc.
3. Weighting: Raw results are adjusted to ensure the sample is representative (by age, gender, region, past vote, education, etc.)
4. Reporting: Results are published with a margin of error (typically ±2–3 percentage points)

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Types of Polls

Type	Description
Voting intention polls	"If there were a general election tomorrow, which party would you vote for?"
Leader approval polls	"Do you approve or disapprove of the Prime Minister's performance?"
Issue polls	"What is the most important issue facing the country?"
Tracker polls	Regular (daily/weekly) polls tracking trends over time
Exit polls	Conducted on election day as voters leave polling stations — generally the most accurate

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The Influence of Polls on Elections

1. Media Coverage

Polls dominate media coverage of elections. "Horse-race journalism" — reporting who is ahead and by how much — often crowds out policy analysis.

2. Tactical Voting

If polls show a close race in a particular constituency, voters may adjust their behaviour (e.g. voting for the candidate most likely to defeat the one they least want).

3. Bandwagon and Underdog Effects

• Bandwagon effect: Voters may be more likely to support the party they think will win
• Underdog effect: Some voters may sympathise with the party trailing in polls
• The evidence for both effects is mixed

4. Party Strategy

Parties use private polling (as well as public polls) to shape their campaign strategy, messaging, and resource allocation.

5. Morale and Mobilisation

Polls can affect the morale of party activists and supporters. If a party appears to be losing badly, its supporters may not bother to vote (demobilisation).

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Notable Polling Failures

Election/Event	What Happened
1992 general election	Polls predicted a Labour victory or hung parliament; John Major's Conservatives won a majority. Led to the establishment of a polling inquiry.
2015 general election	Polls consistently predicted a hung parliament; the Conservatives won a majority of 12. The British Polling Council launched an inquiry, which identified problems with sampling and weighting.
2016 EU referendum	Most polls predicted Remain would win; Leave won 51.9%. Online polls were generally closer than telephone polls.
2017 general election	Most polls predicted a comfortable Conservative majority; Theresa May lost her majority. YouGov's MRP model was one of the few to correctly predict the close result.

Why Do Polls Get It Wrong?