The political blogging site Left Foot Forward, which represents itself as an “evidence –based analysis of British politics” yesterday published a bold extrapolation of recent political polls (below).

If these projections hold, says Left Foot Foward, Labour will overtake the Conservatives in the week of the election – if it’s on May 6, as has been widely predicted.
 
Politics doesn’t work like this. Labour was down, now it’s up (a bit), the Conservatives were up, and now they’re down (a bit). By what magic Left Foot Forward believes these trends can be represented by a straight line and then extrapolated, it does not explain.
 

 
As John Rentoul, chief political commentator of the Independent on Sunday, comments in his blog: “The reasons why people vote or change their minds about voting are driven by the challenges faced by politicians and how they respond to them. Like stock markets, poll, ratings, even for the Labour Party, can go down as well as up”.
 
And not necessarily in straight lines, he might have added.