5.5 million bubbles of polling froth

According to YouGov, 40% of people think Ed Miliband is doing well as Labour leader. A week ago, only 28% thought this. So, in an electorate of 46 million, this means that about five-and-a-half million people have changed their minds. In one week. On the basis of a few headlines and TV clips about one speech.

Do you believe that?

Actually, I do. But what I don’t believe is that any kind of firmly held opinion could change so quickly and easily among so many people.

A lot of survey responses are just froth on the surface of an uncommitted mind, as suggested by this ingenious study that manipulated people into justifying answers that they hadn’t really given.

And this latest boost to Miliband’s ratings? It may well harden, at least in part, but only if he keeps up a better performance and gets decent coverage for it. The longer a vague impression lasts, the firmer it becomes.

But my general rule is that sudden improvements in polling are normally an illusion – like the way that Nick Clegg’s 2010 campaign surge led to only slightly more votes, or the way that Gordon Brown’s impressive honeymoon ratings were blown apart by something as flimsy as an opposition tax promise.