My wife would certainly attest to the fact that I have a particular abhorrence of spiders. It is hard to know how it originated. Our progenitors no doubt had some fear of spiders and even more so of snakes. They, as hunter gatherers would routinely have encountered these potential threats. As a result over the millennia we would have developed an instinctual fear of these venomous creatures. Today, as I have often stated, we would be better served to have instinctual fear of electricity sockets, speeding motor vehicles and all manner of drugs. But of course, we don’t have sufficient evolutionary history with these threats to have embedded any instinctual responses.

So what is the likelihood that I might die from a spider bite or a snake bite – despite my irrational fear it is, of course, quite small. And herein lies the problem I wish to discuss with you this week. We all seem to have irrational fears that bear no relationship to the probability of their occurrence.

We have seen in the press a lot of debate about the danger of sharks. Unfortunately in recent times there have been a number of lives lost to these frightening predators. Yet if we were to look at the inherent danger from a more holistic point of view we would find that the likelihood of losing a life to a shark attack is less than the likelihood we might get struck by lightning. (Although I was impressed by a letter in the paper the other day from a West Australian man, who boasted that he and sharks had found out how to accommodate each other – he didn’t go into the water and the sharks didn’t go into the pub!)

The population at large seems to have no great capacity to weigh up the probability of various outcomes. For example, the physicist Garrett Lisi estimates that the risk of dying from a spider bite is less than 1 in a 100 million. This risk is so small that it is counterproductive to worry about it. Millions of people die each year from stress-related illnesses. It seems therefore likely that the stress of worrying about being bitten by a spider is a greater risk than being actually bitten by a spider!

It is possible that sometimes our irrational fear of some risks result in greatly heightened risks in other areas.

Let’s take a (relatively) recent and dramatic example.

It was one of those historical occasions. Like the death of JFK. Or the first moon landing. Everybody seems to remember what they were doing when we first saw those chilling pictures on 11 September 2001. Who could believe it? Airplanes being deliberately flown into the twin towers of the World Trade Centre in New York. Almost 3,000 people lost their lives as a result of this wanton act of terrorism and more than 6,000 were injured.

 

We watched in disbelief as the TV stations played it over and over. Our senses were assaulted by the anguish and the horror of the spectacle. Responsibility for the heinous crime was claimed by Al Qaeda, a Sunni Muslim extremist group founded in Pakistan and active throughout the Middle East. Many of us had hardly heard of them, and those of us who had, believed its activities were confined to traditional Muslim communities. It was a major shock that they could impact so violently on a modern industrial society. And it was beyond comprehension that some organisation would willingly and with obvious pride want to associate itself with this heinous crime.

 

There were of course some unintended consequences as a result. For example as a result of the terrorist attacks on the World Trade Centre airport, security was greatly enhanced. Consequently our frequent exposure to x-ray body scanners in airports could perhaps increase our risk of cancer more than the likelihood of being the victim of a terrorist attack!

Another consequence emanated from the general public’s reluctance to fly after this traumatic event.

After the World Trade Centre disaster, around the world there was a pronounced reluctance to fly. Even though, assuming some ongoing terrorist activity, flying was still statistically a far safer way to travel than most others. But we don’t get live coverage of car crashes. We make movies of highjacking airplanes and committing other terrorist atrocities. But we seem to just shrug off motor vehicle accidents as something expected and perhaps unavoidable.

 

Gerd Gigerenzer is a German psychologist who studies the use of bounded rationality and heuristics. He studied the impact of Americans flying less and driving more after the Twin Towers attack. This is what he had to say:

 

“This is a good example of where intuitions and gut feelings can go wrong, even cost your life. We know that after 9/11 many Americans stopped flying. What did they do instead? Did they stay home or did they drive? I analysed the data and published a study showing that for 12 month after 9/11 miles driving was up 5 percent more than usual. And that cost the lives of about 1500 Americans. They lost their lives while driving in an attempt to avoid the fear of flying.

 

These people were motivated by a kind of emotional gut feeling of fear that is well known. The fear is not of losing your life – it’s the consideration of where many people can die at one time. So that doesn’t apply to driving. More than 40,000 people lose their lives in the US on the road every year, but not many care much about it. But if it’s a large number (as per the Two Towers atrocity) – about 3,000 at one time – that’s really what causes fear.

 

The reason may be evolutionary. In times when humans were in small bands, wandering around, the loss of many lives at one point would have threatened the survival of the whole group. That kind of gut feeling is still around – people are afraid of catastrophes, killer bees from West Africa and other kinds of things. Here’s where an education of the public can help to avoid these fears the next time something happens.”

 

Gerd Gigerenzer published a paper comparing the number of road fatalities before and after the 9/11 event. In the US the shift from airline transport and road transport lasted merely one year. Road fatalities increased dramatically in the year after the terrorist attacks and then returned to normal statistical levels. Gigerenzer calculated the increased number of Americans killed from this switch of transport options. The number was 1,595.

 

As I suggested above the population at large does not seem to handle the concept of probability well. For example if I toss a coin and it comes up heads seven times in a row, most believe that the possibility of tossing tails is enhanced. But of course it is not! One every occasion we toss the coin the possibility of heads or tails is equal. The likelihood of tossing heads seven times in a row is very small (1 in 128) but that has no bearing on the next toss of the coin.

It is also a source of some amusement to me as every year police departments announce a war on traffic accidents. If the numbers improve, even though within the statistically normal variations that probability would allow, they trumpet their success! If the numbers get worse, even again within the probability that normal statistics would allow, they gnash their teeth and exhort the general public to drive more safely!

That people do not understand the laws of probability is evidenced by the fact that so many stand in front of the poker machines in clubs and bars and continue to waste their money!

And so, for various reasons, many of us hold irrational fears. Even those with a reasonable understanding of statistics (among whom I would include myself) allow the impact of our gut feelings and instinctual responses to prevent us from acting rationally when exposed to various forms of danger even when the real probability of its occurrence is low.