National polls, local polls and seat destinations

Eoin O’Malley(4th February, 2011)

The national polls carried out by reputable agencies such as Red C or Ipsos-mrbi are reliable as guides of the likely percentages the parties would get if the election were held at that time. In the middle of a campaign they are even better guides of the eventual result because potential voters are thinking more seriously about how they’ll vote . The polls are never perfect guides because of sampling error (luck of the draw – occasionally you’ll see a rogue poll which seems so out of kilter with other polls that it might be ignored) and there will be differences across polling companies because of differences in methodology. For instance question ordering is important – if people are asked about party leader preferences before party preference this will prime respondents to evaluate the parties through their leaders. Some companies include political weightings, based for instance on past vote and probability to vote – so if you say you’re definitely going to vote, your response is weight more than those who say they possibly will vote.

When the different polls from the different polling companies point to the same thing – as they do now (FG in mid-30s, Labour in low to mid-20s,  FF in mid to high teens and SF in low to mid teens) then we’d be wise to take them as accurate guides. That’s not to say the eventual outcome will look like that. The election campaign could still have an impact.

If we want to see the impact of the campaign and how it might move the electorate over time polls don’t usually help us. Small changes in party support are likely to be down to sampling error. And political parties’ campaigns usually have the impact of cancelling each other out – it’d be nice if we could expose a group of voters only to the campaign of one party and see what happened! But we can see party trends over time and we can observe the impact of major events  (remember the impact the leaders’ debate had for the LibDems in the UK last year.) Because of the different polling companies’ methodologies if we want to observe changes in party support it’s usually best to compare polls with those from the same polling company. Because Red-C is the only company with a regular polls these give the most reliable sense of change. The Irish Times polls yesterday indicated a drop in support from last December but we don’t know whether it was in fact an increase in support from two weeks ago.

The other thing we use polls for is to make seat predictions. If we are looking for seat predictions nationally there’s a good reason to follow Michael Gallagher’s method of calculating likely seat bands for each party. If we want individual constituency predictions or to know where those seats will be delivered, Adrian Kavanagh’s posts offer fascinating predictions and analyses. But with the arrival of so many independents (of various types), new candidates and retirements, I suspect it’s safer to make specific predictions on the basis of local polls than extrapolating from national polls on the basis of 2007 results. For instance Shane Ross’s entry into the race in Dublin South could mean FG won’t win a third seat there, and Fianna Fáil’s weak candidate there makes it less likely that the party will hold a seat.

These local polls are problematic. They have much smaller samples (rarely reported) which drives up the margin of error (also rarely reported). Though there are exceptions, they are not normally carried out by professional pollster who know the impact of different types of questions nor have they usually any idea about sampling methods, which again drives up the potential error, but not in a predictable way. Despite these health warnings they do alert us to potential shocks especially from candidates people outside the constituency had never heard of and weren’t being considered as potential challengers – Tom Gildea in 1997 for instance.

A local poll in the two Kerry constituencies suggests that FF may lose both seats in the county, but that Labour will pick up one in Kerry North, while Kerry South is wide open. In the Sligo Champion Fine Gael is predicted to take two seats in Sligo – North Leitrim, while Susan O’Keefe and the two FF candidates fight out for the third seat (it’s on the paper’s website but behind a paywall). In Laois Offaly an internal FF poll reported in the Leinster Express shows that Sinn Féin’s Brian Stanley should take a seat. As other polls are released anyone who sees them can let us know in the comments section.

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