Tuesday, May 04, 2010

Precisely Wrong

As I write, Sky News are reporting various polls with Tory support between 33% and 37% and LibDem support between 23% and 28%. The parties and commentators hang on every percent with elation or despair.

But they are wrong to do so.

These polls are spuriously precise (which we don't really care about), but not necessarily accurate (which we desperately do). If, for example, a pollster says Tory support is 35%, what they mean is something like this:

"I am highly confident that Tory support is 35%, give or take 3%. When I did the sample. And that is if people are telling the truth."

See those bits in bold text. What they mean is that if you take those numbers as being accurate, more fool you. It's a statistical game and you need to remember that. Don't be in raptures when your party goes up a percent or two on in despair when it's down a percent or two: that may well just be "sampling error".

All you can really conclude from today's polls is that the Conservatives are a bit ahead and LibDems and Labour are neck-and-neck.


So get back to your campaigning, before the Fat Lady sings.

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