In the Times, Phillip Collins says of George Osborne that 'it was hubris worthy of Mr Brown to trust that export growth would be as fast as it needed to be make the Treasury's growth forecasts come true.' This is not the only parallel between the two; Osborne's ragbag of tricksy policies aimed at raising long-term growth also look rather Brownian.

Such similarities shouldn't surprise us. Politicians of all main parties have a lot in common simply by virtue of being politicians. In particular, they are selected to have particular cognitive biases.

What sort of person will want to be a politician? There are three related types:

- Someone who thinks that policy can change society. But - at least in the context of longer-term economic growth - this belief owes more to wishful thinking than the evidence.

- Someone who is overconfident about their chances of success - in terms of either achieving office or doing something useful when they have it. Such overconfidence reinforces the optimism bias, and leads Chancellors - be they Osborne or Brown - to believe they can transform the economy.

- Someone who thinks that individuals can make a difference; the sort of person who thinks politicians are victims of events and circumstance is unlikely to enter politics. This means politicians are prone to the fundamental attribution error, of overweighting the role of agency and underweighting that of environment. Again, this leads them to believe that their own actions can make a difference.

There's worse. Someone entering politics might have these biases. But they are highly likely to be reinforced throughout their career. The fact that you're surrounded by like-minded people who share these biases will generate a form of groupthink. And the fact that the opposing party also shares them will breed a folie a deux, in which one side's delusions are reinforced by the other. (In fact, it's a folie a trois, because the media - with its search for heroes and villains - further reinforces these biases.)

In this sense, the clich'' that politicians are all the same has some validity. There are all the same in some respects because selection effects cause them to share particular cognitive biases.

Now, it would be wrong to say that politicians are unique in having these biases. Most of us are guilty of overconfidence or wishful thinking at least sometimes. It's just that politicians are selected to be more so than others.

Not that they are alone in being so selected. So are company bosses. It's small wonder, therefore, that the political and business 'elites' should be so close to each other. They have a lot in common. The trouble is, they just don't have so much in common with the rest of us.