12/08/2011 12:14 BST | Updated 11/10/2011 06:12 BST

Norway attacks and biases in judgement

Norway witnessed an unprecedented tragedy on 22 July. Anders Behring Breivik's actions demonstrated in a vivid manner how human insanity, propelled by a twisted ideology, can justify the worst atrocities. However, at the same time, the immediate reaction to Breivik's attacks provided an excellent snapshot of how predictable biases affect our judgment under uncertainty.

When the first reports from Norway's capital arrived, the world was trying to make sense of these attacks. Norway was hardly on the top of any list of possible terrorist targets. The Scandinavian nation is famous for its peaceful and tolerant society. So, what went wrong? And, more importantly, who's to blame?

Al Qaeda and the jihadists! Or, that was the consensus until the Norwegian police released photos of a white, ethnic Norwegian as the prime suspect. Yet, before this revelation, the social media were abuzz with rumors about Al Qaeda's involvement in the Oslo bombing. Scores of policy analysts were discovering 'links' and justifying Al Qaeda's choice of target.

In fact, the Wall Street Journal went so far as to publish an editorial, which was later revised, attributing the responsibility for Oslo attacks to the jihadists. It read:

"Norway certainly did not buy itself much grace from the jihadists for staying out of the Iraq war, or for Prime Minister Jens Stoltenberg's demand that Israel open its borders with Gaza, or for his calls for a Palestinian unity government between Fatah and its terrorist cousin Hamas.

Norway can do all this and more, but in jihadist eyes it will forever remain guilty of being what it is: a liberal nation committed to freedom of speech and conscience, equality between the sexes, representative democracy and every other freedom that still defines the West. For being true to these ideals Norwegians have now been made to pay a terrible price."

Why such grave errors in judgment surfaced while, and here's the crucial part, all the available evidence pointed to the opposite direction? Stephen Walt, a Harvard professor of international relations, explains that if anyone had bothered to look at the data, he would have guessed that it was far more likely that a European was responsible for the attacks:

"In 2009, there were fewer than 300 terrorist incidents in Europe, a 33 percent decline from the previous year. The vast majority of these incidents (237 out of 294) were conducted by indigenous European separatist groups, with another forty or so attributed to leftists and/or anarchists. According to a Europol report, a grand total of one (1) attack was conducted by Islamists. Put differently, Islamist groups were responsible for a whopping 0.34 percent of all terrorist incidents in Europe in 2009. In addition, the number of arrests relating to Islamist terrorism (110) decreased by 41 percent compared to 2008, which continues the trend of a steady decrease since 2006."

A possible answer lies in the work of Amos Tverksy and Daniel Kahneman, a Nobel laureate (2002) in economics, who studied systematic biases in humans' intuitive assessments and predictions. One of their main contributions is the identification that, in the presence of uncertainty, we employ heuristics that lead to predictable judgment errors.

Consider the following experiment, reported in their 1974 article: "...subjects heard a list of well-known personalities of both sexes and were subsequently asked to judge whether the list contained more names of men than of women. Different lists were presented to different groups of subjects. In some of the lists the men were relatively more famous than the women, and in others the women were relatively more famous than the men. In each of the lists, the subjects erroneously judged that the class (sex) that had the more famous personalities was the more numerous".

This phenomenon, labeled 'availability bias' or 'bias due to retrievability of instances', demonstrates how familiarity plays a major role in our assessment of subjective probability (i.e. likelihood of occurrence). When making judgments, we characterize more likely events that quickly come to mind, i.e. events that are available or easily retrievable.

However, while availability is usually closely correlated with frequency, this is not always the case. For example, our personal experiences matter. Tverksy and Kahneman explain that people judge the probability that a particular couple will divorce to be higher when divorces are common amongst one's friends and relatives. Similarly, salience affects the retrievability of instances. They note that "the impact of seeing a house burning on the subjective probability of such accidents is probably greater than the impact of reading about a fire in the local paper."

Now let's get back to the original example concerned with attributing responsibility for the Oslo attacks. What comes to mind when we hear about terrorism? The answer is probably Al Qaeda and the jihadists, especially after the striking images of 9/11. Does it matter that jihadists' attacks in Europe are a very rare occurrence? No, because when we judge probability we don't look carefully at the available data but rather base our judgments on what is quickly available in our minds. The fact that less than 1% of terrorist attacks in 2009 in Europe were attributed to jihadists didn't matter at all!

Nevertheless, the use of heuristics in decision making is not entirely problematic. On the contrary, it would be impossible to pass judgments or calculate probabilities in everyday life without the use of such simple rules. However, it is important to be aware of the inevitable biases that arise from their use.