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The Health Secretary Andrew Lansley says he wants to nudge wherever possible and nanny only where necessary.

The "nudge" effect he's talking about is a growing body of evidence about what influences our decisions.

The advocates of nudge say understanding how and why we choose is a powerful tool for influencing behaviour.

Even sceptics accept this behavioural science has a place, but argue there are times where a government just has to act.

The science of "nudge" brings together economics and psychology into the newer discipline of behavioural economics. It focuses not on what the rational choice might be in any situation, but the powerful and often unconscious impulses that shape our decisions.

Many businesses have long understood that this could be extremely useful in marketing. Supermarkets, for example, do extensive research on how the layout of their aisles will alter the choices made by an average shopper.

Companies selling online often set their default option on forms for us to give permission for follow-up marketing e-mails. They know that the default is more likely to be accepted, and fewer of us will remember to actively opt out.

In recent years there has been growing interest from governments grappling with problems that are created, or altered, by the decisions of many individuals.

This includes how many people sign up for pensions and lifestyle choices which lead to health problems requiring treatment later in life.

While the coalition is publicly embracing the power of nudge, there has in fact been keen interest within government departments for several years. Shortly before the election the independent think tank, the Institute for Government, and the Cabinet Office jointly published a report called Mindspace.

It's designed as a guide for policy makers so they can think about how to incorporate this body of evidence into designing policies. The report sets out what is known about the decision making process, from the power of the default to the use of incentives. It is already being used by the new "nudge" unit set up by the coalition government.

One of the co-authors is Ivo Vlaev, a senior lecturer in Psychology at Imperial College London. He says the evidence shows our choices are far less predictable than many policy makers had realised.

"Researchers have demonstrated various types of 'context effects.' How much we value options depends not on intrinsically stable and consistent preferences.

"Instead it relies on the sample of other such options that we think we have at the time of choice or remember from previous times."

Mindspace describes these different context effects. On the simplest level they include factors such as the norm - what we think is normal, based on people like us.

That can alter how much you think it is acceptable to drink, and what you interpret as fat or thin. We tend to dislike short term losses, even if they lead to longer term gains, an example of why dieting is difficult.

This had led to many parts of the NHS in England looking at the use of incentives to make that short term loss more palatable.

Schemes which have been tried in the last couple of years include giving shopping vouchers to people losing weight or to pregnant women who manage to give up smoking. Such incentives can be controversial, but many experts believe they can work.

The government has said it is seriously considering regulating to bring in plain packaging for cigarette packs. This can also be linked to some of the research. By removing the visible prompt from the packet of a familiar brand it is hoped casual smokers would be less likely to buy on impulse.

By and large public health experts accept that this body of knowledge is extremely useful. It can be incorporated into thinking how to persuade people to make healthier choices around food, exercise, smoking and alcohol.

Professor Lindsey Davies, head of the UK Faculty of Public Health, says this approach shouldn't be used to rule out more obvious government intervention when that is needed.

"Look at the smoking ban, look at the difference that's made to lots of people's lives and actually helped them give up smoking.

"We're seeing enormous changes in health already. So there is a place for regulation when it's needed."

The mandatory wearing of seat belts and the introduction of the ban on smoking in public places are two examples where legislation fundamentally altered, and some would say restricted, the choices of individuals.