Drinking, sex, eating: Why don't we tell the truth in surveys?
Many people are under-reporting how much alcohol they are drinking. But what else are we fibbing to researchers about and why do we do it?
"I have the occasional sweet sherry. Purely medicinal."
It is a classic British sitcom scene. An inveterate boozer telling a little white lie about how much they drink to a doctor or other authority figure.
But the tendency to paint a less-than-honest picture about your unhealthy habits and lifestyle is not just restricted to alcohol. People also tend to kid themselves about how much exercise they are doing.
It is understandable that people want to present a positive image of themselves to friends, family and colleagues. But why fib to researchers?
After all, the man or woman from the Office for National Statistics or Ipsos Mori can't order you to go on a diet or lay off the wine.
It is a question that has been puzzling social scientists for decades.
They even have a name for it - The Social Desirability Bias.
"People respond to surveys in the way they think they ought to. It is otherwise known as lying," says Kate Fox, an alcohol and drinking culture expert who has done research for both the government and the drinks industry.
"People also kid themselves about how much they drink, but it applies to most surveys, which is why one has to use other methods to really find out what is going on."
It is a particular problem when it comes to "sins" such as alcohol and food.
Britain is one of a handful of nations - including the US - that has an "ambivalent drinking culture", says Fox. It is particularly prevalent in countries that have had a strong temperance movement.
"We have a morally charged relationship with alcohol, a love/hate relationship. It is a bit of a forbidden fruit."
In countries with an "integrated drinking culture", such as more Latin nations, drinking is a "morally neutral issue, only marginally more controversial than coffee and tea".
It is easy to see why people would want to make themselves look good - even to a clipboard-wielding researcher they have just met.
But what about when the researcher leaves the room? Or hands them a separate questionnaire to be filled in privately? They're all tactics used by researchers to try and iron out the Social Desirability Bias.
"You still want to project a positive image of yourself even if the survey is anonymous," says Bobby Duffy, managing director of Ipsos Mori's Social Research Institute.
The gap between the amount of alcohol being sold in the UK and the amount people said they were drinking, was first observed in the 1980s, he says.
"People have unrealistic expectations about what other people are doing and that does affect how they how they respond.
"They think other people are drinking a lot less alcohol, doing more exercise and having a lot more sex and that changes their view of their own behaviour."
The gap between perception and reality might be particularly acute in the UK, he suggests.
Awareness of healthy eating in the UK is among the highest in Europe, yet the country also has the highest obesity rates.
The key, says Duffy, is to view survey results as part of a bigger picture - and, he stresses, it is still possible to track overall social trends from self-reported surveys.
But if people underestimate how much they drink, do they overestimate how often they have sex?
The sex survey has been a surefire way to boost the circulation of a newspaper or magazine for decades.
Yet there is anxiety among sexual researchers that they are not as accurate as they should be.
"In a large number of these surveys people inflate how often they have sex. They are buying into this idea that great sex is measured by how often you have it," says Petra Boynton, senior lecturer in International Health Care Research at University College London.
"We do have an anxiety about trusting sex research generally, partly because of worries over talking about sex but recently more because of the misuse of the survey tool as an advertising device.
It is hardly surprising, she says, that journalists and the public don't trust sex research:
"What they see shared in mainstream media is not the careful and more balanced work undertaken in social and health research.
"As sex stories on relationships advice in media are pinned on 'statistics', then this allows the dodgy PR polls to be used to tell us how we should be having sex and set up ideas about what is normal."