In 2001, there was a byelection in Tipperary South which Fianna Fáil was expected to win.

The party lost the vote, and afterwards blamed it on an opinion poll published seven days before polling which it claimed had swung the result.

The party tried to introduce legislation that would ban opinion polls in the seven days prior to polling day. But the legislation was withdrawn after a rebellion in the Seanad led by Shane Ross and Maurice Manning.

Could opinion polls really be that powerful? Do they merely act as a weather vane for the prevailing political winds? Or are they themselves capable of brewing up a storm?

The leading British authority on opinion polls, Peter Kellner, is in Dublin this week to address that very question.

Kellner is president of leading British polling company, YouGov, and a former political journalist.

British polling companies have been on the money for recent elections, and Kellner was the first to (accurately) call the Scottish referendum on polling night.

Underestimated support

However, most pollsters there got their call on the British general election wrong this year, underestimating support for the Conservatives.

The theme of his speech on Friday at the View (a Festival of Arts and Politics) event organised by the Temple Bar Company, is: 'Opinion Polls: A Threat to the Democratic Process or a Useful Tool in Ensuring Responsive Government?'

In an interview with The Irish Times in advance of his speech, Kellner said that until recently France was one of a number of countries that banned opinion polls in the week before polling.

He said the paradox was that polling proved very lucrative for the companies conducting them as partners, companies and agencies all commissioned private polls from them.

He said he was not sure if the process is democratic, as only those with power and money had access to such information. If politicians made outrageous claims, it might then be a criminal offence to contradict those claims.

“However, I would not offer the defence that polls do not make a difference. It is possible that information on what people are thinking does have an influence.

Tactical position

“That is particularly true for byelections. It does allow voters to understand the tactical position and switch their votes to ensure a candidate they don’t like is defeated and the candidate they most like wins.

“If they are properly conducted, I basically do not see a problem.”

Opinion polls have evolved from face-to-face interviews at home to telephone and online polling. Kellner has said British polling companies changed their methods after getting the 1992 election wrong (John Major was the unexpected victor).

Different companies have different methods, he says, but the important thing is that all are transparent about them.

He instances ICM Research, which drills into the poll response cohort which says “don’t know” and looks at how they voted the previous time, and then makes a judgment on what they will do.

“It has increased the conservative vote by one or two percentage points, but they are open and honest about this.”

YouGov polls online. Most people have an online presence, but there are small pockets of the population (elderly working-class women for example) who might be under-represented in the online population, but YouGov takes steps to allow for this in its recruiting, sampling and weighting procedures.

Late swing

The evidence in the Scottish independence referendum was there was a late swing towards the status quo that was captured by later polls. Something similar had happened in a similar referendum in Quebec.

So how did pollsters get the British general election so wrong? The polling companies have jointly commissioned research to investigate the reasons why.

"The first point I would make is that when we interrogated our evidence, people were saying: 'I don't like the Conservatives and I am worried about the National Health Service, but I think David Cameron would be a better prime minister than Ed Miliband and the Tories are better on the economy'.

"Some of those said they would vote Labour and voted Conservative, even though the broad attitude was dislike.

“That maybe explains more than half the three points, but I am not persuaded there was ‘don’t knows’ who broke to the Tories.”

Peter Kellner was to speak at the Irish Stock Exchange at 12.30pm on Friday as part of the Temple Bar Arts and Politics Weekend.