April 4, 2015


[How often do you have sex? How long for? Where and when, and do threesomes figure? Meet the man who has studied our sex lives in intimate detail - and has now written an eye-popping new book]

Professor Sir David Spiegelhalter has been investigating the works of numerous
sexologists in his quest to separate fact from fiction Photo: REX FEATURES
A quick look at the bookshelf nearest Professor Sir David Spiegelhalter’s desk gives you plenty of clues as to the academic’s recent field of endeavour. He laughs as he declares that some of them “are really lurid”. So it would seem; on a swift recce I note How Big is Big, Sexual behaviour in Britain, With the Hand, The X-Rated Bible and a Victorian Guide to Sex, alongside more familiar tomes by Alfred Kinsey and Shere Hite. Spiegelhalter admits “My Amazon recommendation list is a complete disgrace!” If I didn’t know better, I would think this was the study of a dedicated sexologist, rather than that of an eminent statistician trying to sift through and elucidate what’s valid, or not, in sex researchers’ data. Because that’s the task the Professor has set himself in his new book Sex by Numbers: to scrutinise the surveyors of sex and their methodology and see what truths we can really take away from their work – if any.

His area of study has been so recherch√© that some of it has had to be conducted under supervision. When Spiegelhalter was looking in to the work of US social scientist Katherine Bement Davis (who researched the sex lives of several thousand women) in the Cambridge University Library, he discovered that although it was published in 1929, “It’s still treated as a real top shelf book. You have to order it and you’re not allowed to take it out of the room… they’ve never changed its classification.”

On first meeting, it’s fair to say Spiegelhalter appears a somewhat unlikely figure to spend many months sifting through the output and conclusions of sexuality’s great, and often wildly eccentric, pioneers. He has the measured, slightly abstracted manner of the career academic, not to mention the cluttered study, and, as Winston Professor of the Public Understanding of Risk at Cambridge University, he is more likely to be seen explaining why flying is still, statistically speaking, a safe way to travel, than discussing the ins and outs of physical intimacy. One of the first admissions he makes to me is, “I am a bit pedantic,” but then who wants anything less in a statistician? However, when the Wellcome Collection planned this year’s major exhibition, The Institute of Sexology, which explores the work of pioneering sexologists, the curators talked to Spiegelhalter’s publishers about a tie-in book, to “cut through the confusion and explore the truth” behind their rhetoric and numbers.
Professor Sir David Spiegelhalter pictured with some of his research
One of the key phenomenons Spiegelhalter investigates is how unreliable assertions and figures about sex end up in the public eye, before being extensively recycled. When I ask him if he has a pet hate amongst so-called “facts”, he cites the old chestnut that “men think about sex every seven seconds”, which has no basis in any scientific study. I tell him I loathe the spurious surveys that variously announce women are having the best sex of their lives in their 30s, 40s, 50s and 60s, which clearly tell us nothing about desire, but much about how we all live in the moment. I don’t admit to him that when I was editor of The Erotic Review magazine I doctored a poll of our readers, so that Margaret Thatcher became the second sexiest woman who had ever lived (rather than the 5th) and that the results were reported as far afield as Germany and Portugal. But I am sure the Professor can sniff out my charlatan soul. He is like a ferret after the rat of dodgy data, declaring with a glint in his eye,“This book pretends to be a book about sex, but actually it’s a book about biases in statistics.”

Spiegelhalter warms to his theme, explaining that, “The statistics of sex is a particularly challenging area, because it’s private, it’s secret, we don’t know what’s going on… we cannot directly observe the things we’re interested in. So, if we’re interested in sexual behaviour, we have to make inferences, either by asking people by surveys and doing our best to make sure that’s accurate, or by inferring what behaviour there is by things we can measure: like how many babies or born, or how many abortions there are, or how many people get diseases.” Accuracy being the Professor’s key theme. He has even created his own star system in the book for the methodology used to gather data on sex. 4* ratings are those rare numbers we can assume to be reliable, such as the stats around births, marriages and divorces and anything which people are legally obliged to register. 3* stats are only “reasonably accurate”, because they rely on those questioned telling you the truth. Even with tried and tested systems for eliciting honest answers, you can’t guarantee all the people will be honest all of the time. 2* data can “be out by quite a long way”, often because the person conducting the research isn’t truly objective, while those questioned about their sexual habits aren’t representative of the population as a whole. 1* numbers are quite simply “unreliable” and a zero rating is awarded to anything that’s obviously made up, like the 18th century physician Samuel-August Tissot’s eye-boggling assertion that losing one ounce of sperm is more debilitating than losing 40 ounces of blood.

Several other Goliaths of sexual research are felled by Spiegelhalter’s ratings. Kinsey’s blockbuster studies only merit a 2 and the Professor says, almost mournfully, that although in some ways he admires Kinsey “his stats are pretty ropey”. Spiegelhalter’s eyes light up with mischief when he recounts how three renowned US statisticians of the 1950s, including John Tukey, tried to take Kinsey to task when Sexual Behaviour in the Human Male was published in 1948. However, the sexologist refused to answer any questions at all until all three men had taken his detailed questionnaire on their sex lives. As one author’s revenge on three pedants, it takes some beating. Spiegelhalter shakes his head in bemusement and says: “These statisticians are my absolute heroes. It’s extraordinary what they had to go through.”

There are even sterner reprimands for the data in The Hite Report (since much of it gleaned via women’s groups and interested bodies), which scores a dodgy 1. But, happily for the UK’s national bedroom stats, NATSAL, the British National Surveys of Sexual Attitudes and Lifestyles, scores a respectable 3, due to the care taken to have a properly random selection of respondents, a home visiting system and ensured confidentiality. The Professor applauds the “huge effort to elicit accurate answers about behaviours that might be considered rather transgressive.” He cites the fact that, “masturbation wasn’t in the 1990 survey. It was included only in the last two surveys,” making me reflect how the late Philip Larkin might have written a poem on the topic: “Onanism began in 2001, between the Kubrick film and Facebook fun.”

“Probably the question about how many sexual partners you’ve had is the one that attracts most attention, because the difference in response between men and women shows they can’t both be right,” Spiegelhalter admits. Quite so. Blokes seem to brag a bit, while we females tend to forget a few inconvenient truths. Furthermore, in one enlightening experiment, when women were wired up to fake lie detectors, their answers on the question were a far closer match to the men’s. The Professor points out that some of the disparity will also come down to any given individual’s personal definition of “sex”. Bill Clinton declared of Monica Lewinsky he “did not have sexual relations with that woman” and a 1999 survey from Indiana University showed 40 per cent of respondents believed, like the President, oral pleasure didn’t constitute sex. However, NATSAL would disagree: for the purposes of its research, oral engagement is very much part of sex. You begin to see how finickity this sex terrain gets in terms of reliable data.

Even so, Spiegelhalter believes that the three NATSAL surveys, 1990-2012 show some clear trends. We Brits do experience a 7-year itch (when relationships are most likely to break up) and, startlingly, established couples are having less sex than we were when the first survey was conducted. Some people point the finger at social media as our iPads get taken to the bedroom and passion neglected, but the figures don’t disclose the “why”. We are far more tolerant across all age groups on the question of same sex relationships than we were two decades ago. However, we are much less accepting of infidelity – or, as Spiegelhalter tactfully terms it, “extra-dyadic sex.” He he has no intention of being judgmental about the sexual behaviour of others (unless coercion is involved) believing it’s not the statisticians job to observe behaviour, not comment on morality. He warns against the temptation of making simplistic causal links, which might lead to overly simplistic remedies “with unintended consequences".

Indeed, Spiegelhalter’s entire life’s work is tilted at steering politicians and the public away from bad data and unfounded deductions. He tells me “Britain has got a fantastic reputation” in statistics and that the subject is “only going to become more and more important… I feel rather strongly that part of our education of everybody should be able to help us know how many statistics are constructed and the manipulations that can be done to them.” Quite so: particularly when we have a General Election on the near horizon. With a Knighthood awarded in 2014 for services to statistics, I think we can rely on Sir David to gently steer us in the right direction. As I gather my possessions to leave his study, with its tranquil view of the Cam, I can’t resist asking if he would ever offer up the intimate details of his own life to a stray researcher? No!” he says emphatically, “Mind your own business”. Before relenting a little, “Not unless it was a proper official confidential survey.” I leave with a fantasy cage fight in my head: Professor David Spiegelhalter vs Professor Alfred Kinsey. And I’m putting my fantasy wager on the British don to come out on top.

The average energy expenditure by young people during sex is 85 Kcal - the equivalent of a couple of Jaffa Cakes.

The average heterosexual couple reports having sex three times a month between the ages of 16 and 44 - this has decreased from five times a month over the last 20 years. The proportion of men who claim to have successfully self-felated