While Ebola itself has been successfully contained in some West African countries, stories suggesting an outbreak of Ebola on this side of the ocean have been mounting: A woman was spotted at Washington, D.C., Dulles airport in a homemade full-body hazmat suit. In New Jersey, two children were kept home from school because they recently had visited Rwanda (an African country not affected by Ebola). Even Mexico has fueled the fear, rejecting a visiting Carnival cruise ship because one passenger had handled an Ebola patient’s blood work. Evidence of widespread fright is more than anecdotal. A recent poll from the Harvard School of Public Health found that nearly 40 percent of Americans believe they or their immediate family are at risk of contracting Ebola during the next year. The stresses accompanying this epidemic of fear — the anxiety,  the stigmatization and the economic impacts — are far more dangerous than Ebola itself, at least within the United States. So why do we allow ourselves to fall victim to them?

Forty years of research by myself and others on the perception of risk can answer that question. People’s sense of risk has little to do with mathematical probability. Instead, we judge the level of risk associated with an activity, technology or disease to be extreme and unacceptable if the hazard:

  • is new or unfamiliar.
  • is perceived as increasing and unbounded.
  • is invisible and uncontrollable.
  • evokes feelings of dread.
  • has fatal outcomes.
  • is seen as not adequately understood by experts.

Ebola hits all these risk-perception hot buttons.

Not only that. We also know that most risk perception is determined by gut feelings rather than by reasoned analysis. Again, Ebola stands out, as frightening images and associations become synonymous with its very name. However, reliance on feelings to assess risk is not necessarily irrational. This form of fast thinking enabled humans to survive the long course of evolution, before scientific methods and quantitative risk assessment were available.

Nevertheless, this sophisticated “feelings compass” that guides us through our daily decisions can sometimes give misleading readings. For example, research has demonstrated that, when the consequences of an event, such as becoming infected with Ebola, evoke feelings of dread, the likelihood of that event occurring may be greatly overestimated. The mind interprets the dread associated with the consequences to mean that the event is likely to happen, regardless of its improbability. Legal scholar Cass Sunstein has characterized this as “probability neglect” and has linked it to costly overprotection against very remote threats of terrorism. He observes that when probability neglect is at work, people’s attention is focused on the bad outcome itself, and they are inattentive to the fact that it is unlikely to occur.

Another well-documented fact about risk perceptions is that, valid or not, they have strong social and economic impacts. Through a process known as “the social amplification of risk,” people scan media reports of harmful events for signs that there may be more and possibly greater trouble ahead. For example, are there hints that those in charge of managing the risk lack competence and cannot be trusted? Do we believe they will inform us accurately about how we personally can control our risk from this type of threat? Trust is fragile; it is hard to earn but easy to lose in the wake of even a single misstep. Signs of mismanagement trigger ripple effects in society that can prove far more costly than the direct toll of death and morbidity from the hazard.

The risk landscape is littered with casualties from social amplification. When Tylenol capsules were poisoned with cyanide in 1982 resulting in seven fatalities, it cost the manufacturer more than $100 million to recover its market share. In 1989, a TV program accusing the Environmental Protection Agency of failing to protect children from alar, a suspected (but unproven) carcinogen, caused the market for Washington State apples to collapse overnight, inflicting an estimated $100 million loss on apple growers. A few years later, the market for British beef collapsed when its consumption was suspected to cause a human variant of mad cow disease. These and other risk-perception crises similar to Ebola triggered costly ripple effects because stigma and distrust entered the picture. In some cases, costly protective measures like tamper-proof packaging for drug products were enacted to prevent already unlikely events from happening again.

Though excessive measures may be costly, it does not necessarily mean they are futile. It is better to err on the side of overprotection in the face of dread risks to address public fear. The precautions taken in screening passengers at airports after Sept. 11, 2001, attest to our determination to push the probability of another massive terrorist attack as close to zero as possible, in recognition not only of the potential direct casualties of such an attack but also of its social, political and economic impacts. Experts have derided some of these extreme precautions as “security theater,” but such measures do maintain people’s trust in the safety of air travel. Planes fly full despite the threat of terrorism.

The bottom line is that cost-benefit calculations that inform decisions about the official Ebola response need to incorporate the impacts of risk perception, in addition to the traditional costs associated with preventing illness and caring for severely ill people. When this is done, procedures that would not pass a less inclusive cost-effectiveness test become advisable, such as an aggressive policy towards screening and monitoring travelers entering the United States by air.

There is no easy answer to the question of how far to go with precautions to address public fear. There is quite a lot of pushback against quarantine of returning medical workers, by scientists and medical authorities as well as the workers who would be subject to it. They argue that it would be counterproductive, discouraging health care workers from traveling to Africa and allowing it to spread further. At this time, screening and monitoring people who may have been exposed to Ebola seems a proper compromise. If new cases continue to emerge, more restrictive policies, perhaps including travel bans, will need to be considered. The recent decision by the Obama administration to more closely monitor passengers arriving from Liberia, Sierra Leone and Guinea, strikes a balance between precaution and feasibility and makes sense from a risk-perception standpoint as well as a medical one.

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