Bias in the spotlight: availability bias

We often judge the likelihood of an event, or frequency of its occurrence by the ease with which examples and instances come to mind. This is known as availability bias.

More emotionally impactful, disastrous or memorable events are likely to be considered more probable. Things that are more commonly or vividly shown in the media; violent murders for example, or a disaster like 9/11, are a lot easier to remember than less noteworthy or salient news. A minor accident in the workplace or a statistic is not as memorable as a tornado.

Because newsworthy events can be readily recalled from memory, the availability bias causes people to rate them as more likely to happen than they are in reality. As a result, vividly memorable (and widely reported) events like murders, plane crashes and shark attacks are considered much more common than they really are, because they are reported much more than other less sensational causes of injury or death.

In contrast, there are many other things that appear harmless, yet on investigation turn out to pose a bigger threat than we might think. For example, around 10,000 people a year in the UK are injured in their homes in incidents involving socks and tights – seemingly innocuous items. However, incidents of electrocution – something people view as a significant danger – number only around 3,000 each year.

It also turns out that cheerleading is a far more dangerous sport than skiing and rugby: 66% of “catastrophic” sporting injuries suffered by women in the US (resulting in permanent disability or chronic medical conditions) are caused by cheerleading. And in universities the figure is even higher, at 70%.

Daniel Kahneman illustrates availability bias with a couple of examples in his book, Thinking Fast and Slow:

• “Because of the coincidence of two planes crashing last month, she now prefers to take the train. That’s silly. The risk hasn’t really changed; it’s an availability bias.”
• “He understates the risks of indoor pollution because there are few media stories on them. That’s an availability effect.  He should look at the statistics.”

As Kahneman says at the end of the second illustration, if we hope to avoid availability bias we must make decisions based on statistics or factual evidence. The extent to which estimates of causes of death can be warped by availability bias and media coverage can be seen in a study by Paul Slovic and his colleagues which showed that people judge death by car accident to be more than 300 times more likely than death by diabetes whereas, in reality, at the time of the study, it was only around four times more likely.

So, before we make a decision or judgement based on the horrors that come easily to mind, we should try investigating the facts first. It might help to make us a little more rational.

Crawford Hollingworth is founder of The Behavioural Architects