UCL Health of the Public


Sex by numbers

Join hosts Doctor Xand van Tulleken and Dr Rochelle Burgess for Season 3, Episode 3 of Public Health Disrupted with Prof Cath Mercer and Prof Sir David Spiegelhalter.


The National Surveys of Sexual Attitudes and Lifestyles - Natsal - are among the largest surveys of sexual behaviour in the world, broadly representing the British population. What methodology is used to acquire such intimate knowledge from someone and why is this data so important?


“A remarkable number of claims you see in newspapers and magazines about sex are essentially made up.”

What does the average British person think about sex? For over 40 years the Natsal surveys have been recording sexual data, capturing striking changes in our behaviour and sexual lifestyles across the decades. They have been pivotal in the population measurement of the social, behavioural and biological aspects of sexual health. Its evidence has underpinned public health policy, practice and research for over 25 years.

So, how do you get someone to open up about something that’s so deeply personal and sensitive? Who decides what questions need to be asked and how much can we rely on the reported data? As a co-lead at Natsal, Prof Cath Mercer shares insights into the methodology and the survey’s broadening remit while Professor Sir David Spiegelhalter presents his argument for disrupting public health messaging.


Professor Cath Mercer is Professor of Sexual Health Science at UCL and co-lead of UCL’s Centre for Population Research in Sexual Health and HIV. A statistician and demographer by training, Cath is recognised internationally as an expert in developing and employing robust methods that advance the study of sexual behaviour - one of the most socially-sensitive areas of scientific inquiry. For more than 20 years, Cath has played a key role in delivering Britain’s National Survey of Sexual Attitudes and Lifestyles (Natsal), one of the largest and most comprehensive surveys on sexual health in the world. She is now co-leading the fourth Natsal. Cath also champions myth-busting and promoting the public conversation around sex, including - rather nerve-wrackingly - through stand-up comedy sets for UCL’s Bright Club and her TEDx talk ‘Let's talk about (real) sex’.

Professor Sir David Spiegelhalter is Emeritus Professor of Statistics in the Centre for Mathematical Sciences at the University of Cambridge. He was previously Chair of the Winton Centre for Risk and Evidence Communication, which aimed to improve the way that statistical evidence is used by health professionals, patients, lawyers and judges, media and policy-makers.  He was very busy over the Covid crisis.  He presented the BBC4 documentaries “Tails you Win: the Science of Chance”, the award-winning “Climate Change by Numbers”.  His bestselling book, The Art of Statistics, was published in March 2019, and Covid by Numbers came out in September 2021.  His career highlights include appearing on Desert Island Discs in 2022, and in 2011 coming 7th in an episode of BBC1’s Winter Wipeout.

Find out more about the NatSal Surveys on their website https://www.natsal.ac.uk/

Public Health Disrupted with Rochelle Burgess and Xand Van Tulleken is produced by Buckers at Decibelle Creative, find her on Instagram: @decibelle_creative and here: https://www.decibellecreative.com