How (and why) we lie to ourselves about opinion polls

A strange ritual takes place on Twitter most evenings at around 10.30 p.m. Hundreds of political anoraks start tweeting the results of the YouGov daily tracker poll due to be published in the following day’s Sun. Some of them are neutrals, but the majority are politically aligned and will only tweet those results that show their party in front.

I often wonder what the point of this is, even though I’m guilty of it myself. It’s not as if anyone is going to see the tweet and say, ‘Ooh, I wasn’t going to vote Conservative, but now that YouGov has them two points ahead I’ve changed my mind.’ I can think of only two sensible reasons for doing this, both quite weak.

The first is it has a mildly demoralising effect on your opponents. Occasionally, I get replies from enraged lefties saying, ‘Well, what do you expect from a Murdoch rag?’ That counts as a successful bit of trolling in my book. The second is it steadies the nerves of the people on your side. For both Labour and the Conservatives, discipline during the election period is essential, and there’s no better backbone-stiffener than a four-point lead, even if it only lasts 24 hours.

But anyone giving these reasons for crowing about good polls is engaging in post-hoc rationalisation. What they’re really doing, I think, is trying to defend their belief that their team is going to win, not just to other people, but also to themselves. Publicising favourable opinion polls isn’t intended to make the result they want more likely. Rather, they’re producing ‘proof’ that the result they’ve already foretold is going to happen.

In other words, it’s a form of confirmation bias, which psychologists describe as the tendency to seize on evidence that supports your point of view, while ignoring or rejecting any evidence that contradicts it.