Welcome to Understanding Uncertainty

Welcome to the site that tries to make sense of chance, risk, luck, uncertainty and probability. Mathematics won't tell us what to do, but we think that understanding the numbers can help us deal with our own uncertainty and allow us to look critically at stories in the media.


Sex by Numbers, by David Spiegelhalter, is now available for purchase!

Details of reviews, interviews, (and errors) are all featured here.

Do you have a coincidence story? David Spiegelhalter is collecting them over at http://cambridgecoincidences.org.

Elsewhere on UnderstandingUncertainty:

Jeremy Hunt, the Guardian, and the importance of getting the stats right

On Thursday November 19th the printed version of the Guardian had the headline “Experts dispute Hunt's claim on weekend hospital treatment“ [online version here]. But it was not only Health Secretary Jeremy Hunt who gave a misleading statement – the Guardian also made a serious error about statistics.

HRT, breast cancer, and the framing of risks

The way that risks are 'framed' can make a big impression on their apparent magnitude. The controversy following the recent report by NICE on hormone replacement therapy (HRT) provides a fine example.

Is it fair that a single bad outcome should label a surgeon as an outlier?

Surgeons are increasingly subject to statistical monitoring, and named results may be made publicly available. But consider a surgeon in a low-risk specialty who has had a successful and blameless career, until a combination of circumstances, possibly beyond their control, contribute to a single patient dying. They then find they are officially labeled as an ‘outlier’ and subject to formal investigation, all because of a purely statistical criterion. Is this fair?

A visualisation of the information in NHS Breast Cancer Screening leaflet


The current NHS Breast Screening leaflet contains some fairly complex information which can be summarised using the graphic below.

Why live interviews are a particular challenge for statisticians.

I like doing live interviews for radio or TV – it’s exciting and they can’t edit what you say. The programme is almost inevitably running late, so last Saturday morning when I did an interview for Radio 4’s Today I remembered my media training and had prepared carefully to get my points over before they cut me off.

Was anyone right about the pre-election polls?

There has been much wailing and gnashing of blogs since the dismal performance of the pre-election polls last week. These had confidently and consistently predicted a rough tie in vote-share between Labour and Conservative, but when the votes were counted the Conservatives had a 6.5% lead.

Comparison of vote-share BBC Poll of polls on May 6th, and actual results on May 7th.

What is your 'effective age'?

How old are you?

You might, quite reasonably, calculate your chronological age as the time elapsed since you were born. But what is the effective age of your body?

Sensationalist promotion by the World Cancer Research Fund

Today the Daily Telegraph featured the powerful headline "Just three alcoholic drinks a day can cause liver cancer, warns new study" , based on a press release from the World Cancer Research Fund headed “Three alcoholic drinks a day can cause liver cancer, new research finds”.

Misleading conclusions from alcohol protection study

The Daily Mail today declared that "Drinking is only good for you if you are a woman over 65", while the Times trumpeted that "Alcohol has no health benefits after all".

But these headlines are without serious foundation, and through no fault of the journalists.


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