Actually, I haven’t been watching you. I just cobbled together some assumptions about what you might have done on Saturday night, based on what I perceive to be pretty normal behaviour. We’ve all done the occasional beer-and-jalfrezi overload, so where’s the harm?

This is the basis of social norms theory, and it may hold the key to a long-standing paradox in public health: why do we persist in doing things that we know are bad for us? It could be, the theory goes, because we believe that everyone else is doing them. And, when it comes to some things, we think everyone is doing them, even when they’re not.

Such misperceptions can become self-fulfilling — if I mistakenly believe that most middle-class working mothers swig a bottle of merlot when they get home, I’ll feel less guilty about doing the same. My false belief could be a first step on the road to alcoholism.

A similar phenomenon has been found among college students. Most of them — around 70 per cent — overestimate the frequency with which their peers binge-drink. The more distorted a student’s misperception, the more likely he is to binge-drink himself. The truth is, students are pretty moderate drinkers. And there is good evidence to suggest that when students wise up to their peers’ moderate approach to alcohol, they cut down the booze. The urge to conform overtakes the urge to binge-drink.

Writing in The Scientist, the McDonnell Social Norms Group — a collective of academics drawn from such institutions as Yale, Stanford and Columbia universities — blames similar misperceptions for propagating problems as diverse as resisting antibiotics, racism and voter apathy (it has become fashionable, for example, to express political disillusionment by not voting). They point to the human need to imitate — we like copying each other, which is why trends in fashion, art and music travel at lightning speed.

The group believes that public health workers now need to link with sociologists to get health messages across: “Our ability to forge collaborations between those who promote good practice and those who study how practices spread is critical to improving human welfare, public health and the global environment.”

This approach, it seems, is already paying dividends. The National Institute on Alcohol Abuse and Alcoholism reports that in a number of US colleges where an accurate picture of student drinking habits had been communicated, hard drinking fell by a fifth over a short period of time.

• AN UNUSUAL group of people has been identified as being at risk of contracting bird flu: voodoo priests. One popular ritual, conducted to appease the spirits, involves the priest tearing out the throat of a chicken with his teeth, which, unsurprisingly, involves a fair amount of chicken blood.

  The H5N1 strain has reached Nigeria, and the fear is that it will spread to neighbouring Benin, where 60 per cent of the seven million population practise voodoo. Benin’s Agriculture Ministry has said it will now target “convents”, the houses where the rituals are performed.

• READERS OF this column are made of stern stuff. So I can tell you that, in about five billion years, this planet will be no more. The Sun will run out of fuel, swell into a red giant — this is when the planet either fries or freezes — and then retire for eternity as a shrunken white dwarf.

  But Nasa would prefer us not to dwell on such trifles. When Marc Kuchner, of the Goddard Space Flight Centre in Maryland, was about to reveal the discovery of comet dust around a white dwarf, he prepared a press release about seeing the ghost of a star that was once like the Sun. And then: “I cringed when I saw the data because it probably reflects the grim but very distant future of our own planets and solar system.”

  The sentence was deemed inappropriate, and deleted. “Nasa is not in the habit of frightening the public with doom-and-gloom scenarios,” a honcho from Nasa HQ said rather tartly. I, on the other hand, have no such qualms.

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