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IPFS News Link • Voting and Elections

Election 2015: can we trust the polls?

• theguardian.com

On Saturday evening, the Labour flank of the Twittersphere erupted in jubilation as a YouGov poll placed Ed Miliband's party four points ahead of the Conservatives.

Pundits were rushed to TV studios in Westminster on Sunday to explain the reasons behind the sudden Labour surge – some even went as far as arguing the party was now entering majority territory.

A few hours later, at 10pm on Sunday, a ComRes poll was published showing the exact opposite picture.

Labour's joyous bubble burst, the Tories exulted.

Over the next five weeks this pattern will be repeated many more times as the number of polls published increase in the runup to 7 May.

This raises two questions.

How can two polls be so different?

Polls carry a margin of error and levels of confidence. For example, a poll of 1,000 people has a margin of error of about plus or minus three points and a confidence interval of 95%. In theory, this means 95 times out of 100 the figure in one poll will be within three percentage points of what it would be if you surveyed the entire population.


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