Will weighting changes knock 2-3% off Labour’s position?
With the chances of Labour winning most seats at the next election down to just 53% on the betting markets could we see further price changes if the polls continue to show a Tory recovery?
The next scheduled poll is from Populus early next week and punters should treat the headline results with some care until we have had time to analyse the detail because we might be about to see a change in the way the Populus calculates its figures.
At the General Election in May Labour had a 3% lead over the Tories in the GB popular vote. Yet when ICM, YouGov and Populus seek to weight their findings to ensure that their samples are representative they assume a much bigger margin. In recent months ICM has been weighting so its samples have a 6% Labour 2005 General Election lead while Populus for the Times surveys has been working on a massive 11%.
If Populus change these weightings then there could be a move to the Tories which is based on methodology – not on actual opinion. Conversely if there is no methodology change in we could see a Labour position that is reinforced by what I believe is an over-generous weighting correction.
What happens is that the pollsters ask how those surveyed voted last time and then adjust their figures in line with what actually happened but with a correction to deal with “misremembering”.
The pollsters argue, with some justification, that more people will say they voted Labour on May 5th than actual did so. It is the scale of this that I have taken pollsters to task for in the past and any change in the way this is done will have a direct impact on the final polling numbers.
The importance of this was seen in December when Populus was showing a 3 point Tory deficit compared with Tory leads ranging from 1-9% from the other pollsters. If the firm had been operating on the same basis as, say, ICM then, Labour’s lead would have been down to a one point.
My understanding is that the Populus approach is under review and it is possible that we could see changes incorporated into the firm’s January survey next week.
Given that the Times usually gives splash treatment to its monthly Populus poll punters should be wary about coming to quick conclusions. Populus is by far and away the best of the firms when it comes to being transparent and is always ready to enter into a dialogue when issues arise and usually responds very quickly.