Thanks to Bradluen who came through with the R code I begged for in my previous post. It’s available here. He comments:
Currently the lines don’t go through the actual election results. However, just upweighting the election results in the Loess gives weird results. In fact I kind of think Loess isn’t quite right here. Use another smoother?
Here’s the resulting chart from the Wiki polling data showing aggregated poll results since the 2005 General Election:
The black lines are election dates.
Why is Labour trending down, even though most of their post-election polls have been improvements on their election result? My guess is all those low poll results just before the election are weighing the distribution. Should the polls be weighted by date? Update: changed the parameters of the script to generate a slightly different graph.