March 26 2020

Risk and uncertainty during the COVID-19 pandemic

Tom Dickins, Professor of Behavioural Sciences discusses the impact that human behaviour is having during COVID-19 pandemic.

There is a distinction to be drawn between risk and uncertainty. Risk refers to a known probability, which can be interpreted as a chance of something happening within a set of things or as an expectation of a unique event.  Uncertainty implies an unknown probability.  Risk data is hard won, and very often imperfect. But living under uncertainty should be common.

At the time of writing, the world is in the grip of a pandemic caused by a novel coronavirus. This virus leads to a respiratory disease called COVID-19, which on current data has a high death rate. The World Health Organisation (WHO) has predicted the death rate will settle at 3.4% of the global population if the virus goes unchecked. The data on recorded cases, recoveries and deaths is assiduously collected. 

For an unbiased statement of the data, the Worldometer Coronavirus[1] page is very useful. From the data on this site, it’s possible to calculate the current estimated risk of catching COVID-19 and dying from it at a national level. This data changes daily, and so one could track risk in light of changing policy and time. On the 23 March 2020 in the UK, I had a 0.0005% chance of dying from COVID-19, assuming equality of both access to infection and immune response across the population. Those assumptions would not stand up to much scrutiny, as we already know the probability distribution for death is skewed by age, health and, some predict, by socioeconomic status. Not all of us can eat well and afford to isolate from the general population.

The data is useful, but imperfect

The data is constantly changing as the population responds to the situation.  We are actively engaging to diminish the pandemic. Moreover, very few people will have the time or resources to properly interrogate it and calculate sound risk estimates for infection and death. 

Instead we rely on experts to do this work for us, to assess risk and to adjust policy. Just this week (23 March), the UK was subject to stringent measures[2] to impose social distancing and isolation in the hope that this behavioural intervention will reduce the reproductive rate (R0) of the virus from 2.5 to below 1. 

The current R0 means that every infected person will infect a further 2.5 individuals. With an incubation period of about five days, and an average of 30 days per month, we have six rounds of infection waves in the first month alone from the first infection. That is 2.56, leading to 244 new infections from that initial person. If the R0<1 then the virus will vanish from the population, unable to replicate. But any reduction below 2.5 will be hugely beneficial in terms of the reduction of stress on the health service (Table 1, Figure 1).

Table 1

R0 New infections in first month month (rounded)
2.5 244
2.25 130
2.00 64
1.75 29
1.50 11
1.25 4
1.00 1
0.90 0.5

R0 Values for the novel coronavirus and the estimated number of infections caused in the first month alone. The value of 2.5 is thought to be the natural R0 for this virus. Social distancing and isolation can reduce this value and the table shows the estimated effects of reduction on first month infections. 

Figure 1

Possible R0 values (starting with the natural R0) plotted against new infections caused by an initial infection in the first month. Social distancing measures can cause R0 to fall, with positive implications both for strain on health services and the possible eradication or management of the virus. 

When we add in the data about R0 and incubation we can see that the estimated death rates within a population like the UK will grow, as pulses of infection and disease develop.  So my point estimate for 23 March was really just that, an impoverished estimate of risk for that day.

The economic uncertainty

Not only is there uncertainty about mortality, there is economic uncertainty.  An unchecked pandemic would overwhelm health services, lead to deaths from otherwise treatable diseases as a result and reduce the workforce significantly through sickness. The imposed social distancing and isolation in force in the UK and elsewhere will also significantly impact our economy through disruption. That disruption is to almost every aspect of our lives and we do not know how long it will need to continue in order to gain control of the pandemic.

Given that humans in the UK, and most of the rest of the world, acquire key resources for survival through economic activity, any threat to their cash flow, any threat to their economic value, is a direct qualitative and quantitative threat to their long-term survival. We should expect humans to have become highly sensitive to any cues that indicate increasing economic uncertainty. 

Of course, this will be unevenly distributed across socioeconomic classes, by definition. Wealthy individuals will have surplus cash to buffer stochastic cash flow for finite periods of time. Poorer individuals will be living in something close to, if not precisely like a hand-to-mouth cash economy.  Financial stochasticity for these people could spell rapid disaster. HM Government in the UK is aware of this, and of the longer-term impact of letting people financially fail. They have promised significant financial support[3] to buffer the costs of social isolation policies, but the details of this support have been slow in arriving and no precise timeline for delivery has been published.

Can we adapt to these changes?

Animals, including humans, have a number of adaptations for dealing with stochastic food supply, the most fundamental of survival issues.  These include fat deposition and food hoarding or caching, both of which are methods of storing energy for future use[4]. Those outcomes can occur directly after a reduction in foraging success, but also in response to indirect cues such as changes in weather conditions that might indicate reduced food availability. 

Under uncertainty, animals are also more likely to become focused upon cues that might predict food, becoming what Anselme and Güntürkün refer to as sign-trackers. This sign-tracking under uncertainty is also associated with a greater willingness to discount the future and seek out more immediate term rewards, even if the pay-offs are less than those available on delay. This aspect of foraging is the equivalent of delayed discounting in economic situations, where participants will favour £10 tomorrow rather than £20 in two months. An obvious interpretation is that £10 now is deemed an essential need if life is hand-to-mouth.

The financial uncertainty caused by the current pandemic amounts to uncertainty about where meals and other resources are going to come from at some point in the near future. From what we know of animal foraging, the observations of panic buying in the supermarkets[5] should not necessarily surprise us.  People have been perplexed by some of the items that have been particularly subject to hoarding, but toilet rolls and pasta take care of basic hygiene and rapid calorie intake. 

If you are uncertain of food supply, calories are what should count just to keep you running.  Nutrition is a second order issue. 

We might further predict that panic buying is more likely to occur within populations at greater risk of financial ruin, or at least those with experience of such events in their meaningful cultural past.

Uncertainty plays a role in public health policy

We have no clear idea of how long social isolation will need to be pursued in the UK, or elsewhere in the world. There are considerable emotional and mental health costs to cutting a primate species from its networks. 

Necessarily people will feel these costs and the hope is that they will understand them as imposed by delays to some future where our health and survival will have been protected to some large extent. But if uncertainty is the backdrop to processing these policy requests then more immediate rewards may be sought, and those rewards could effectively amount to violations of the policy. 

One reason for the “lockdown” in the UK on 23 March 2020 was because many people, already many days into moderate social disruption, were aggregating en masse and increasing transmission risks in public places.  The general population did not behave as if it understood the risks, but rather as if it were frustrated. HM Government, along with Italy’s and elsewhere, realised that institutional impositions were required to control this.

Given this propensity to discount futures when under uncertainty, policy makers perhaps should pay some heed to building meaningful reward structures into their interventions. In the UK, on 23 March, the Prime Minister invoked wartime language, saying all citizens were enlisted in the fight and our particular job was to stay at home and minimise contact. It was a language of group defiance in the face of threat, and not without utility. 

But wars involve bombs and visible damage, after the politics from which most citizens are excluded have failed. They start and they are obvious. Our current situation is to fend off an invisible enemy whose attack, whilst rapid, is hidden from us until it is too late. We are being asked to act before the event and those acts are costly. The only cues we really have to attend to are the massive changes in our lives and they invoke uncertainty.

It is hard to know precisely what rewards would work or would be possible. But anything that enhanced social interaction would be a place to start. Whilst the financial support offered is essential to keep businesses afloat, investment in the provision and improvement of internet connectivity would be a great asset. Not all individuals are connected, and of those that are a proportion will have bandwidth that will be insufficient for new demand. Meanwhile, the overall network is bound to be under pressure. Leaving it to the companies to resolve this alone is perhaps a poor idea. Just as leaving it to the supermarkets to resolve food supply issues, in light of panic buying and reduced workforce due to COVID-19 sickness, is odd[6]

If this were a war, those things would become under ministerial control and our propensity to cache food would be attenuated by rationing.





[4] For an excellent review and analysis see Anselme, P., & Güntürkün, O. (2019). How foraging works: Uncertainty magnifies food-seeking motivation. Behavioral and Brain Sciences, 42, E35. doi:10.1017/S0140525X18000948



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