Sex By Numbers: The Statistics Of Sexual Behaviour

David Spiegelhalter Profile Books €19.50

We are, collectively, cutting down on sex. In 1990, heterosexual men and women aged between 16 and 44 were having sex, on average, five times a month. You might have thought this was on the sluggish side, but 10 years later the figure had dropped to four times a month, and by 2010 to just three times a month. In short, sex has become the Betamax of leisure activities.

David Spiegelhalter offers a number of explanations for this libidinous nosedive: more of us live alone, we are increasingly distracted by computers, we find it easier to watch it than to do it, and we are busier and more exhausted than ever.

But having read this book, another explanation springs to mind: the time we used to give to sex we now set aside for completing sex surveys. Hey presto! Desire is transformed, as if by a particularly gloomy form of magic, into maths.

Sex By Numbers attempts to navigate a path through these percentages, some reliable, others less so. Here is a selection: – 26% of women answering the

Cosmopolitan survey in 1980 said ‘women on top’ was their favourite sexual position.

– 12% of people aged between 16 and 44 report having concurrent partners in the past year.

– 34% of women report a lack of interest in sex lasting at least three months in the preceding year.

– 6% of Irish 60-year-olds say they have never had a sexual partner.

– 25% of 13 to 18-year-olds say they have sent a sexual image.

– 14% of Americans aged between 55 and 85 use medicine or supplements to improve their sexual function. – 45% of men wish they had a larger penis. – 26% of Norwegian men born between 1927 and 1934 have visited a prostitute, compared with: 6% of Norwegian men born between 1975 and 1984 have visited a prostitute.

After a while, this storm turns into a blizzard, and before long it becomes impossible to concentrate for more than a second or two on any individual statistical snowflake as it falls and dissolves.

I found all the Scandinavian statistics a particular burden: to be honest, it’s hard to get worked up either way about all those Norwegians who are either visiting or not visiting prostitutes, and if 75% of those Finns who went in for S&M last year employed handcuffs then, though this may be great news for Finnish locksmiths, it’s on the irrelevant side for the rest of us, unless we are planning to have a couple of Finns to stay in the near future (‘Have you remembered your key, Lars?’)

It turns out that many of the most fascinating or alarming sexual statistics must be taken with a pinch of salt. For instance, years ago, I read that one in six American men who had been brought up on farms had had sex with a farm animal. Since then, I’ve seen this statistic every two or three years, always presented as though it were gospel truth. Irritatingly, it was never made clear exactly which type of farmyard animal – woolly or feathered, horned or hoofed – was the chief object of desire, but, as statistics go, it was nonetheless peculiarly haunting, and I would find myself surveying the characters in the homely TV series The Waltons with renewed interest, wondering which of the deceptively fresh-faced Walton boys had had it away with a duck.

But now Spiegelhalter informs us that the trailblazing sex statistician Alfred Kinsey, who originally gave us this snippet from The Farmer Sutra, was not wholly to be trusted, and that many of his most famous statements – for instance, that a man’s sex drive peaks in his late teens, and a woman’s in her 30s – were based on no evidence at all.

In fact, much of this book involves pouring cold water over hot statistics. For decades, we have been hearing that, in the favoured phrase of pub bores the world over, ‘statistics prove’ that men think about sex every seven seconds, yet Spiegelhalter has been unable to find any such statistics. However, he does quote a study in which 283 psychology students in the US were given clickers for a week and told to click every time they thought about sex. The male students estimated in advance that they thought about sex five times a day, but they clicked on average 19 times a day; the women guessed that they thought about sex three times a day but their clicks came to 10.

But even this survey is not wholly to be trusted: 283 psychology students hardly constitutes a broad cross-section of society, particularly as psychology students are, in my experience, peculiarly furtive, skulking around in the corners of rooms, nursing their own dark thoughts.

Spiegelhalter demonstrates, over and over again, how difficult it is to get people to talk honestly about their sex lives. By and