What is it about polling the third party?

Just look at the figures in the panel above showing the Lib Dem shares in the latest surveys from the six firms that carry out regular national voting intention opinion polls. All but Populus are from surveys that have been published in the past week.

How can you possibly have a situation with such a range of shares from the six different pollsters? This is important because the broad trend in most surveys has been a small fall-back in the Conservative share, a chunky increase in Labour’s numbers with the Lib Dem share having suffered the most.

But one firm, ICM, is recording very different numbers and this is a pattern that we see month after month. Are ICM right and the other pollsters wrong or is it the other way round?

A quick glance at the UKPollingReport list of surveys since the 2005 general election underlines the point that ICM invariably has the best figures for the Lib Dems. Why?

All the pollsters have different ways of processing the data and the ICM mathematical approach is probably the most friendly to Nick Clegg’s party. But that is not enough to explain the often quite substantial differences that we see so often.

I have looked at this before and am now even more convinced that it is down to the way the questions are put and the actual words that are used. Firstly ICM respondents are asked: “Some people have said they would not vote in a new General Election, while others would go and vote at their polling station. I would like to know how certain it is that you would actually go and vote in a general election?” This gets over that this is a serious matter but is non-judgemental about non-voters.

Then the key voting intention question is asked in this form: “The Conservatives, Labour, the Liberal Democrats and other parties would fight a new election in your area. If there were a general election tomorrow which party do you think you would vote for?” In Scotland and Wales the SNP/PC options are also listed. Here I think that breaking it down into two sentences helps and the the way the list of parties is introduced is very different from the other pollsters.

Thus MORI does not ask the voting intention question straight away but kicks off with “How would you vote if there were a General Election tomorrow? Conservative/Labour/Liberal Democrat/Other?”

With Populus it is: “If the general election was tomorrow, which party would you vote for? Would it be [rotate order] Conservative, Labour, Liberal Democrat, or another party – or would you not vote at all?” The certainty of voting questions comes second.

ComRes kick off by asking how people voted last time. Then they go into the certainty question and the third point that is put to respondents is: “If there were a general election tomorrow, would you vote Conservative, Labour, Liberal Democrat or some other party?”

Whatever it is intriguing to see how what may seem such a trivial matter has such an impact on the outcome.

Mike Smithson