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Poll Holes

You may not be sick of the election yet, but give it time. One of the more depressing aspects of elections is how little coverage is given to discussions of the merits of different policy options or the plausibility of the teams on offer, and how much is given to treating the election as a horse race. The 2011 election was somewhat different, but that’s because Ireland was in peculiar straits and people suddenly cared about Ireland’s bond yields and such stuff. Now that people aren’t so concerned the media is also reverting to type.

The big feature of election-as-horse race is the opinion poll. They are useful for voters who can use them to consider which potential coalitions are likely. They are useful for parties which can better understand the concerns of voters and failings in their campaigns. They are especially useful for newspapers which can make an opinion poll fill a few pages, even when nothing at all has happened.

Though there are concerns as to the accuracy of polls in recent elections across Europe, they remain the best barometer of public opinion we are likely to have. But because papers are in the business of making the ephemeral seem note- worthy there is a temptation to read too much into polls. To avoid falling into this trap, here are some pointers to keep in mind:

1.  Polls draw samples, and the size of the sample matters. Samples only work because of the probability that they are representative of the population (which is what we really care about) though comprising a relatively small number of respondents. A poll with 1,500 respondents will typically be a more accurate representation than one with 900. With a sample of about 1,000 we are pretty certain that the parties’ real support is in a range around what is reported. This is often about +/-3%. Movements within this Margin of Error (MoE) really might be random, not based on any movement in support for the parties in the population. So: look at the sample size. Many constituency polls have small samples, which increases the margin of error to rates that make the poll wholly questionable.

2.  Sometimes we see interesting results and the media gets very excited. One poll in the 2014 Scottish referendum showed the Yes side in the lead, though all other polls showed a narrow but consistent lead for the No side. There was a frenzy. The likelihood was that this was a ‘rogue poll’, which isn’t to say it was a dishonest poll. When we are pretty certain that a party’s support is in a range (say +/-3%), we mean we’re confident that it is in this range 95% of the time. About one in 20 polls will be wrong. Unfortunately we don’t know which ones they are. But if a poll is very interesting, then it’s likely to be wrong. To avoid getting excited about potentially rogue polls, look at the trends. If a number of polls show a party going up in support, and it’s sustained over time, then we can conclude they’re capturing real movement.

3.  Just because many opinion polls agree about a level of support doesn’t mean that they are right. Polls in the UK election had the Tories and Labour neck and neck for much of the campaign. The MoE assumes perfect random sampling. In practice opinion polls rarely use pure random sampling. Different companies identify and approach respondents in different ways, but all have some selection bias. That is certain groups are more likely to respond than others. This would be fine if these groups all had similar opinions. But they don’t. Older, middle-class men are harder to get to respond than younger, politi- cally active people. This is what caused the failure of polls in the UK to detect the Tory lead. Tory voters weren’t ‘shy’ – embarrassed to admit they voted Tory; they were just less likely to say Yes when asked to respond to a survey. Unfortunately there’s not a lot the lay person can do about this, except retain scepticism. Even when we get accurate poll numbers Ireland offers other challenges. The nature of the electoral system means that converting percentage support into seats is difficult. It is even harder now because the fragmentation of the party system means looking at past trends isn’t all that useful. Also, partly because of the gender quota legislation, many parties have more can- didates than they would like. This splitting of the vote means that while we can be reasonably confident of the first two or three seats in most constituencies, after that the large number of competitive candidates makes predicting the final seats little more than a coin toss.


Dr Eoin O’Malley is senior lecturer in the School of Law and Government, Dublin City University. If we assume polls in Ireland have the same problem as those in the UK and under sample people who are “content”, and if we assume that larger parties get a seat bonus, and Sinn Féin struggles to attract transfers, then on the basis of recent polling numbers, here are my predicted seat ranges for the parties.

Fine Gael  59 ±5 seats

Fianna Fáil  34 ±4 seats

Sinn Féin   25 ±4 seats

Labour   14 ±3 seats

We can be even less certain for smaller par- ties, especially for the Greens and Renua, who may return no TDs. Green 1 seat, Renua 2 seats,  Social Democrats 3 seats, AAA/PBP 5 seats, Independents 15 seats