I like to think that I’m a rational person and that I make reasoned decisions on the basis of a considered weighing up of all the information. This is important, as sound decision-making is vital for the safety of me and other people in the mountain sports that I do. The truth is that I am as vulnerable as everyone else to my decision-making being distorted by biases that lead to less than rational thinking.
Confirmation bias is the tendency people have to accept information if it supports what they believe and to reject information if it contradicts these beliefs. This is because people give more weight to information that supports their existing beliefs and are more likely to look for such information. Conversely, confirmation bias means that people tend to give less weight to information that challenges their existing beliefs and are less likely to look for it. If they do find such disconfirming information, people are inclined to explain it away or attempt to discredit it.
All this makes someone experiencing confirmation bias sound a bit like the sort of opinionated person it is not much fun to get into a debate with in a pub. However, confirmation bias is very natural and so common that we have probably all experienced it many times in the past. Confirmation bias is an unwitting process – it’s not the same as someone deliberately selecting or shaping facts to support their beliefs or an argument that they are making. Issues arise because this common cogitative bias can have potentially serious consequences.
Confirmation bias can be a real challenge for scientists as it can lead them to accept too readily data that supports their hypotheses and to discount data that doesn’t fit these hypotheses. This undermines the validity and reliability of their results. Confirmation bias can also be a plausible explanation for why some business or political leaders have confidently made bad decisions on the basis of questionable evidence. Most of my experiences with confirmation bias have been when I’ve been navigating in the mountains.
I’m a bit of an old school mountain walker in that I rely on a map and compass and very rarely use a GPS. Obviously, map reading involves a lot interpretation and judgment in understanding the map and its relationship to the landscape I’m in. Confirmation bias can kick in when I conclude that I’m at a particular point and then interpret the landscape around me to fit that conclusion. I decide, for example, that because I think I’m at a particular bend in a stream, then the wood to one side of me and the peak to the other, have to be the wood and peak shown on the map as next to the stream bend I’m believe I’m standing next to. If there are any discrepancies between what is around me and what the map shows is around where I think I am, confirmation bias means that I explain them away. So, if the crag I can see looks higher or the wrong shape to the crag as it is shown on the map, I might assume the difference is simply due to perspective or a trick of the light. Sometimes confirmation bias can even make me go as far as to conclude that the map must be wrong or that the map’s scale means that it doesn’t show the details that would confirm my conclusion about where I am.
The risk is that even a small error in navigation can become compounded by confirmation bias and I get lost. For example, on the basis of my conclusion that I’m at that bend in a stream, I head off in what I think is the direction I want to go. As I walk along, I look for the features that the map shows me should be on my desired route and confirmation bias leads me to believe that I see them. So the map shows me using a stile to go over a wall, before the path starts to climb and I pass the remains of an old building. When I get to a stile, I see this as confirmation that I’m on the right path. I discount the fact that the path isn’t climbing as steeply as the map suggests. I assume that the reason I haven’t got the remains of the building is that it is further than it seems on the map and that’s that just a little further on. All the while I’m going further and further away from where I want to be. It’s only when enough disconfirming information builds up that I stop and re-evaluate where I am. This disconfirming information is usually a dramatic difference between where I think I am and the actual landscape, e.g. that the ground should be rising up on my right if I am where I think I am, but it’s rising on my left.
Although, thankfully, it doesn’t happen to me that often, confirmation bias has done things like sending me part way down the wrong ridge and happily walking for twenty minutes down a valley because I missed my turn. At best, this is annoying and time wasting. At worst, navigation errors like this can be dangerous. They can mean that you may find yourself walking towards corniced edges or cliffs. Even just by forcing you to have to backtrack or find a different route, they can mean that you don’t get down before dark or find yourself out in a storm. My experience is that confirmation bias is more likely to kick in during these types of situations. This is because confirmation bias seems to influence you more easily and more quickly when the information you have to make a decision on is more limited, like in a whiteout or when the cloud brings visibility down to a few metres.
I’ve been aware of these risks for a while, but it was only when I was recently doing research for my Masters dissertation that I learnt the cause and the name of it. Unfortunately, what my research found is that there is no sure way to stop confirmation bias. It’s a natural human reaction and creeps into your thinking without you being aware. The only real way to counter it is to be aware that it may happen and repeatedly question your own conclusions. Actively seeking disconfirming information also helps. In particular, regularly checking your compass against the terrain and the map can correct inaccurate decisions, e.g. realising the ridge I think I want to go down runs South West instead of the North West that the map shows as the direction of the ridge that is on my route.
I’ve become better at navigation by doing these things and I seem to fall prey to confirmation bias less often. However, on those occasions when confirmation bias has sent me the wrong way, and I start scrutinising my map to work out where I really am, I try to console myself by thinking that good navigation isn’t about never being off track. Good navigation is about realising you’re off track as quickly as possible and knowing how to get back on track.
This is the definition of confirmation bias provided by The Skeptic’s Dictionary.
If your plane gets lost you’d better hope there’s an orienteer on board
This blog post from the British Psychological Society describes an experiment that highlights how confirmation bias can affect how aircraft pilots navigate. It’s a bit worrying if you are someone who flies regularly.
A great post on the You Are Not So Smart blog that looks at the frequency illusion and confirmation bias. It includes descriptions of experiments that have highlighted what confirmation bias can do.
Nickerson, R.S. (1998) Confirmation bias: a ubiquitous phenomenon in many guises, Review of General Psychology, 2(2), pp.175-220.
This is the best of the various journal articles I read on confirmation bias during my Masters. It describes the evidence for the various forms of confirmation bias and gives examples of how confirmation bias can happen in practical situations.