In order to translate measures of relative risk, such as odds ratios or hazard ratios, to the more easily interpretable changes in absolute risk, we need baseline risks: the proportion of people in the ‘unexposed’ group who experience the outcome of interest. This will help make sense of the real magnitude of the risks reported in research and to be able to communicate its relevance to wider audiences.

Unfortunately, baseline risks are not readily obtained for case-control studies: a fairly common design in which people who have experienced the outcome are identified (the cases), and matched to some extent (say…

Kevin McConway (The Open University)* and David Spiegelhalter (University of Cambridge)**


The coronavirus pandemic has brought an unprecedented demand from the media for statistical commentary. Whereas a trip to a studio for a radio or TV interview was once an exciting novelty for a statistician, the seller’s market over the pandemic means that many requests have to be turned down, and the rest fitted in with family life at home.

While it is always gratifying to be wanted, we have personally faced many challenges in our media work, and here we try to distil our experiences into a list of tips. These are aimed at statisticians who are willing to engage…

The Joint Committee for Vaccines and Immunisation (JCVI) has released its priority list for getting a Covid vaccine, which is as follows:

  1. residents in a care home for older adults and their carers
  2. all those 80 years of age and over and frontline health and social care workers
  3. all those 75 years of age and over
  4. all those 70 years of age and over and clinically extremely vulnerable individuals
  5. all those 65 years of age and over
  6. all individuals aged 16 years to 64 years with underlying health conditions which put them at higher risk of serious disease and mortality


After nearly 45,000 Covid deaths in England and Wales, we can see that people of different ages have been exposed to dramatically differing risks. Fatalities among school-children have been remarkably low. Taking women aged 30–34 as an example, around 1 in 70,000 died from Covid over the 9 peak weeks of the epidemic. Since over 80% of these had pre-existing medical conditions, we estimate that a healthy women in this age-group had less than a 1 in 350,000 risk of dying from Covid, around 1/4 of the normal risk of an accidental death over this period.

Healthy children and young…

Kevin McConway (The Open University) and David Spiegelhalter (University of Cambridge).**


The article ‘An analysis of SARS-CoV-2 viral load by patient age’ by Jones et al. claims that “viral loads in the very young do not differ significantly from those of adults. ”, and the authors “caution against an unlimited re-opening of schools and kindergartens in the present situation. Children may be as infectious as adults.” It has been widely reported as implying that viral loads in children are similar to adults, and yet the data in the article show children between 1 and 10 having on average 27% (conservative 95% interval 8% to 91%) of the viral load of adults…

As COVID-19 changes from being seen as a societal threat to a problem in risk management, it is essential that we get a handle on the magnitudes of the risk we face, and try to work out ways to communicate these appropriately. Note that I am only covering the lethal risks, not the potentially important consequences of illness or treatment.

When discussing the risks surrounding COVID, it is very important to carefully distinguish —

  • The risks of dying from COVID-19, among people who get it (known as the Infection Fatality Rate IFR ). …

The Office for National Statistics (ONS) released the latest data on death registrations at 9.30am on April 21st, covering the week ending April 10th (week 15). Headline statistics include

  • 18,516 deaths recorded, which is an excess of 7,996 deaths over the 5-year average of 10,520 for that week.
  • 6,213 (78%) of these excess deaths have COVID-19, which means that (22%) did not — much lower than the proportion (41%) in the previous week.
  • 34% of all registered deaths had COVID-19 mentioned on their death certificate. This proportion was highest in London (53%) and lowest in the South-West (19%)
  • 58% of…

In a popular blog published on March 21st (which seems a lifetime ago), I argued that the estimated mortality rate of people whilst infected with Covid-19 was very similar to the average risk that people of the same age experienced over a whole year. Both Covid and annual background risk vary hugely within age-groups, with most of the lethal risk being held by people who are already frail. An additional bold assumption that this average property held at the individual level would lead to a very simple interpretation: Covid could be considered as packing what amounts to your current annual…

Note added 2nd May 2020. Some people seem to be interpreting this article as suggesting that COVID does not add to one’s normal risk. I should make it clear that I am suggesting that it roughly doubles your risk of dying this year.

An article by Nick Triggle on BBC Online raises the issue of whether many deaths from COVID-19 would have occurred anyway as part of the ‘normal’ risks faced by people, particularly the elderly and those with chronic health problems who are the main victims of COVID. To provide some background, I’ve had a look at how much ‘normal’ risk COVID seems to represent.

It’s always useful to remember that we’re all going to die sometime, and the rate at which we do so is faithfully recorded in the life tables provided by the Office For National Statistics.

These provide annual…

Just to be on the safe side

There’s been some dire headlines about the current outbreak , such as ‘Virus Panic’ from the Daily Mirror last week, featuring one woman wearing a face mask, and reports of hand gel selling out. As a main official recommendation is to wash hands, buying hand gel hardly seems a panic reaction.

David Spiegelhalter

Statistician, communicator about evidence, risk, probability, chance, uncertainty, etc. Chair, Winton Centre for Risk and Evidence Communication, Cambridge.

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