There has been much debate about the accuracy of opinion polls, especially following last year’s British General Election. So how accurate are the national published polls in Ireland?
The table attached shows that the final Irish Times poll prior to the 2007 general election was very accurate and was well within the +/- 3% margin of error with Labour having the largest error of 2 percentage points .
It was a similar story in 2011 with this time the largest error in the Fianna Fáil vote at 1.5 points.
The local elections in 2014 was very accurate for most of the parties with the notable exception of Sinn Féin whose vote was overestimated by five points in the final Irish Times poll at the expense of the Others (Smaller parties and Independents).
The polls measured the decline in the Fine Gael vote from an average of 36% in 2011 to 32% in 2012, 27% in 2013 and 24% in the locals in 2014.
Their poll ratings rose after that and they were up to 27% in 2015 and averaged 28% for the 17 polls (including the two exit polls) in 2016.
The last poll of 2015 had them at 32% and the first poll in 2016 had them at 31%. There were three polls on 7 February and they sent mixed messages with FG at 31%, 28% and 27%.
They were back up to 30% on 9 February. But the first hint of a drop came when they were down to 26% in the Red C poll for the Sun newspaper on 16 February.
The final five polls of the campaign Fáiled to detect the decline in the Fine Gael vote with a range of 27% to 30%. As we saw above the final Irish Times poll is usually the most accurate but not so this time as they were out by 1.5 points with the Sunday Independent the most accurate at 27%. Both Exit Polls were accurate for Fine Gael.
The polls measured the rise in the Fianna Fáil vote from their disastrous 17.45% in 2011 to 25% in the final Irish Times poll prior to the local elections in 2014.
This was a modest rise but combined with the drop in support for their main rivals Fine Gael, they went from a deficit of 19% points in 2011 to a lead of one point in 2014, to become the largest party in local government.
Their poll figures slipped back to 20% for the rest of 2014 and averaged 19% for 2015. They were down to 17% in the final poll in 2015 and they averaged 20% for the 17 polls in 2016.
The Irish Times poll of 4 February measured them at 21% and this was followed by three polls on 7 Feb which sent mixed messages as it did to Fine Gael and had Fianna Fáil at 17%, 20% and 22%, a five-point spread.
They were at 18% in the next two polls followed by 19% on 16 February. The major movement took place in the final polls with two of them at 23% and 22% in another.
But this rise was contradicted by two Red C polls which had them at 18% on 21st and 20% on 23 February. Both Exit Polls underestimated Fianna Fáil support, with the RTÉ one particularly poor at three points adrift.
Sinn Féin support was overestimated prior to the 2007 general election with the final Irish Times poll measuring it at 9%, two points better than they eventually achieved.
The error was down to one point in the general election in 2011 when Sinn Féin won 10% of the first preference vote. Sinn Féin showed a steady increase from 2011 and was up to 18% for both 2012 and 2013. The overestimation in their vote re-occurred in 2014 when the final Irish Times poll had them at 20%, which was five points above what it eventually got and this was at the expense of Others.
Sinn Féins poll rating was back up to 21% in 2014 and was at 20% in 2015. They were at 19% in the final poll in 2015. They started off 2016 at 19%. The three polls on 7th February again sent mixed messages for Sinn Féin as they had done for the two larger parties with ratings of 17% and 21%. Three of the final five polls were within one point of the final outcome. Both Exit Polls overestimated the Sinn Féin vote with Irish Times out by one point and RTÉ by two.
The final polls accurately measured the Labour support prior to the 2007 and 2011 general elections. They had their best election ever in 2011 but that was as good as it got with their decline setting in right away as they were down to 17% for the rest of 2011.
This decline continued through 2012 (14%) and 2013 (10%). They went into single figures in 2014 and their collapse to 7% in the Local Elections was accurately predicted by the final Irish Times poll.
They managed to claw their way up to 8% in 2015 but the writing was always on the wall. The final polls had them between 4% and 8% and the Exit Polls confirmed their near wipe-out.
The final polls accurately measured the Others support prior to the 2007 and 2011 general elections. They got 17% in 2011 and that increased steadily over the next few years to 21% in 2013. Their very good local election performance in 2014 was underestimated by the final polls by a large four points. Their rise continued after the locals and the majority of the final polls had them at 28% which was just short of their final figure of 29.68%.
The campaigns run by the major parties were reflected in the rise in support for Fianna Fáil at the expense of Fine Gael. Fine Gael had a poor campaign and only realised late in the day that they were in trouble and their last minute vote management exercise saved them from absolute defeat.
In contrast Fianna Fáil and in particular Micheál Martin had a good campaign and that was reflected in how close they got to Fine Gael with only 24,884 first preferences separating them in the end.
The over-estimation of the Fine Gael vote combined with the underestimation in the Fianna Fáil vote meant that there was a five-point gap between these two parties according to the final Irish Times poll.
This gap was as high as 12 points with the final Business Post poll. This gave the impression that Fine Gael were going to win this election, hence all the shock in that quarter since.
If the closeness of the race had been detected by the polls, we could have had a different outcome as more of the Fianna Fáil supporters who left them in 2011 may have returned.
A chance to beat their arch rivals would have been all the incentive they needed to return to the mother ship.
They say local elections are not a guide to what will happen in the next general election. Well that myth was well and truly shattered at this general election. The final result of the 2016 general election is a mirror image of the 2014 local elections with Fine Gael and Fianna Fáil exchanging vote share, FG 24.03% in 2011 with FF on 24.35% in 2016 and FF on 25.31% in 2011 and FG on 25.52% in 2016.
Sinn Féin, Labour and Others were all within a point of their 2014 level. Perhaps if some of the parties had taken warnings from their performance in 2014 they may have had a different result in 2016.