There's a link between David Cameron's holiday snaps and the moral panic about migrants. The link is ambiguity aversion.

We've known ever since Daniel Ellsberg's famous experiments that people don't like ambiguity or uncertainty; they much prefer known probabilities to unknown ones.

This is well known in financial markets: "markets hate uncertainty" is a cliche because its true. However, uncertainty aversion matters in politics too - a fact which is, I fear, under-appreciated.

Here are some examples:

- People fear immigration because it creates uncertainty: they are disquieted by the prospect that migrants will change their communities.The strong possibility that these changes will be benign is little comfort.

- Terrorism is effective - in the sense of provoking a repressive backlash - because it creates uncertainty. The facts might show that Americans are more likely to be killed by policemen than by terrorists - but this doesn't matter because policemen are familiar and so cozy whereas terrorists are not.

- Both front-runners in the Labour leadership election are trying to offer Labour members familiarity: Andy Burnham talks of coming from outside the Westminster Bubble whilst Jeremy Corbyn offers policies which are as warmly nostalgic as Subbuteo and Thunderbirds.

- In talking of Jeremy Corbyn's support for nationalization, Peter Kellner says:

If people think he's doing it as a left-wing ideological move it wouldn't be a popular as if, say, David Cameron did it. If David Cameron said "I'm going to take the railways into public ownership" I think people would be dancing in the streets because nobody would accuse him of doing it for a left-wing ideological motive.

What he's getting at here is that the framing of policies matter. "Left-wing ideology" is unpopular because it seems unfamiliar and so creates uncertainty. Other motives - be they pragmatism or vote-grubbing - are more familiar and hence more acceptable; psychologists call this the mere exposure effect. This is how the Overton window works; policies that are outside the window and so rarely discussed appear to be uncertain and thus become unpopular.

- Radio 4's Broadcasting House asked yesterday whether Ted Heath could become PM now - the point being that a single man would now be seen as strange and hence uncertain. It's for this reason that the media presented Ed Miliband as "weird"; they knew instinctively that the unfamiliar is bad. It's in this context that we should regard Cameron's holiday photo. The message is: "Look, I'm a normal, married guy - you can trust me."

And here's the thing. Some politicians are good at exploiting ambiguity aversion for partisan gains: they know to present themselves as regular guys and their opponents as weirdos.

But this is not the only way in which politicians should address the public's aversion to uncertainty. One function of the political sphere should be to provide institutions which help us to cope with uncertainty: a welfare state which cushions us from economic risks; public services which are flexible enough to deal with social change; an educational system and media which help us understand uncertainties. And so on. But it is not clear that these functions are being fulfilled. Aversion to uncertainty, it seems, is something to be exploited for partisan gain rather than addressed as a political problem.

Another thing: it's easy to forget that Ted Heath became Tory leader in part because he offered familiarity. In the early 60s, the upper-class were regarded as out of touch toffs, as exemplified by Mervyn Griffith-Jones question about Lady Chatterley's Lover: "is this a book you would wish your wife or servants to read?" In this context, the grammar school-educated Heath appealed to those wanting "normality".