There are quite a few political betters who are placing their money on the basis that Labour are going to get hammered. That might very well happen and Robert Smithson's new election predictor certainly adds grist to the mill of those who believe that. But while things look grim for Labour, there is real uncertainty over just how bad things are for them. A slight discrepancy has opened up between the pollsters. An apparent gap has opened up between ICM and most of the others. The difference could be the difference between Labour losing and being slaughtered.
Let us look at the evidence since 1 April - a period of nearly 4 months now, so we have a reasonable amount of data. The ICM polling has been as follows (with the Labour rating following the date):
11 July 2009: 27
14 June 2009: 27
28 May 2009: 22
17 May 2009: 28
19 April 2009: 30
Marketing Sciences (apparently effectively ICM under a pseudonym)
16 April 2009: 26
One thing immediately stands out - with the exception of the poll of 28 May, Labour's record is very consistent. If we were judging Labour's performance by ICM alone, we would treat the poll of 28 May as a rogue or as reflecting a spasm of anger at the expenses scandal, which was at its height then. With the exception of that poll, ICM do not record Labour as having dropped below 25% and otherwise are consistently recording Labour in a 26-30% band. The average Labour rating in these six polls is just under 27%.
Now, compare that with all the other pollsters. Populus's results are closest to ICM's. It had six polls in the period, with a Labour high of 30%, a low of 21% and an average of just under 26%.
In the same period, YouGov had 13 polls with a Labour high of 34% (the first poll of the period - otherwise the high was 27%), a low of 21% and an average of just under 25% (without the first poll, the average is just over 24%). IPSOS-MORI had five polls in the period a high of 28%, a low of 18% and an average of just over 23%. ComRes had seven polls, with a Labour high of 26%, a low of 21% and an average of 23%. BPIX also polled three times in the period, with a Labour high of 26%, a low of 20% and an average of 23%. Harris's single poll in the period gave Labour a rating of 20%.
Now, all of these pollsters make grim reading for Labour: they have not exceeded 30% in any of the last 40 polls. But there is a world of difference between Labour tallying 20% or 23% at the next election and Labour getting 27%. For example, if the Tories tally 40% and the Lib Dems tally 20%, on a uniform swing Labour would score 184 seats with 23% (according to Baxter) and 216 seats with 27%. If you sold Labour today at 202 on the SPIN spreads, that's the difference between making a packet and eating cornflakes for the rest of the month. So if you are betting on the spreads or the Betfair party line, resolving this polling discrepancy is important.
The first thing to ask is whether this is just a case of being fooled by randomness. Others better qualified than me can comment on how statistically significant this is, but in the trade-off between certainty of statistical reliability and using the limited information we have available, it seems reasonable enough to me to make deductions from the sample that we have.
So with caution, we move onto the next question: who is right? And here we run into two conflicting schools of thought. Both of them have been espoused by our host.
The first is that ICM are the gold standard of polling and that especial weight should be given to their findings. Our host made this point two weeks ago here:
It has to be said that this post should give even the most exuberant Labour seller pause for thought. If Smithson pere is right and ICM is this accurate next time, Labour sellers sure as hell need to hope that Smithson fils's seat prediction model is accurate.
But what of Mr Smithson's golden rule? This is explained here:
"based on the results of the last four general elections and all three London Mayoral races the most accurate poll has always been the one showing Labour (Ken in 2000) in the least favourable position in relation to the Tories"
This too is based on hard data. So how are we to make sense of these?
It remains possible that both are right. The post from two weeks ago draws attention to Labour polling well before the general election. The golden rule is only tested at the point of an election. That time lag would allow both theories to remain correct.
That is a neat solution, but a little too convenient. I am deeply suspicious about the idea that future polling movements can be derived in advance from current responses. Movements in public opinion are too dependent on events - while the thought of an impending general election may concentrate minds in a partly predictable manner, that will be just one consideration among many that moves public opinion at any given time.
It comes to the same thing in practice, but for now I prefer to place the greatest faith in the pollster with the best past track record. ICM have a great record in predicting election results and it would be foolish to ignore that when deciding which polls to pay most attention to.
However, if Labour really do poll this badly at the general election, I suspect that the seat predictions implied by applying uniform national swing using the results of other pollsters will probably prove more accurate.