Do you trust the opinion polls?

Yesterday there was something of a minor earthquake in political circles when the figures were released for the latest opinion poll by Lord Ashcroft – which showed a quite incredible six point lead for the Conservatives over Labour. To date most polls had showed either a narrow Labour lead, or the two parties running neck-and-neck, so the figures were a quite literal bolt from the blue. But as Mike Smithson on Political Betting pointed out, the figures were also highly confusing, as an opinion poll by Populus showed a five point lead for Labour. They were conducted at the same time – so surely they can’t both be right, can they?

Opinion polls have taken a bit of stick over the years – not least since they predicted a Labour win in 1992 and completely missed the evidence of a fourth Conservative victory. But as Lord Ashcroft himself points out – polls are snapshots, not predictions, and they are only intended to give an indication of the general view of the public. So for those readers who don’t follow the polls, I wanted to share a few remarks to help you untangle this often heavily misused political device.

First of all, let’s clear up the Margin of Error. Politicians often bandy this about to dismiss polls that they disagree with, but it misses the point. The margin of error stresses accuracy – you only need to sample 1,000 respondents (provided the sample is balanced) to get a result that is accurate to within 3% either way – which isn’t bad at all (for those who wonder, you need a sample size more than double to reduce the accuracy to within 2%, and therefore pollsters decide it isn’t worth the expense). Taking the Ashcroft poll for example – the figures show the Tories on 34% and Labour on 28% – but it may well be both parties on 31%, or indeed the Tories on 37% and Labour on 25%. The margin of error simply means that it is not a perfectly accurate measure – but you can’t simply dismiss the figures out of hand.

Secondly, polls are snapshots of opinions. The question respondents are usually ask is “How would you vote if there were a General Election tomorrow?” – but there isn’t a general election tomorrow! If you look at historic polling (I recommend the UK Polling Report website for this – it is very user friendly!) you will observe that incumbent governments do very badly while in government but then recover as the election draws nearer. That is because voters don’t often like what governments do, but when forced to choose at the ballot box, prefer the government to the opposition!

All of these mean that the most important thing is not a specific poll but the overall trend. Politicians are very prone to take an isolated poll and shout about it from the rooftops when it suits them, and then turn around and dismiss another poll when the figures do not suit them. The truth is that polls can be useful for indicating whether a party’s message is sticking or having any impact – if their numbers are generally going up for example, even if the poll is not accurately guessing what percentage they will get in the end, the poll is demonstrating the party is becoming more popular. Based on that, the party that should have the most to worry about is Labour. As I anticipated in an earlier post, there is a swing heading back towards the government, and the Labour lead in the polls has been falling month on month. Phrased another way – their lead is nowhere near big enough for a party looking to win an election in less than five months.

A final word of warning is this – polls predict a national share of the vote, but elections are decided locally at each constituency, and do not account for variations in vote change – while the Lib Dem vote is likely to collapse from 23% to 10% (or worse) their vote isn’t necessarily going to collapse in every constituency – especially where they have sitting MPs. You should not be surprised if there are huge swings to Labour in some of their heartlands for example, but much smaller swings in the marginal seats. So we have to treat opinion polls with care, yes – but they can also be a useful barometer into just how well a party is resonating with the electorate. And at the moment, the barometer is not showing the kind of support that makes me think we will wake up to a Labour majority in May.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s