DANGER - Confirmation Bias

In my previous blog I touched upon a term called Confirmation Bias and how as testers we should be aware of this. I stated that I would put a blog together on the subject so here it is.

I should start by defining what confirmation bias is.

Confirmation bias refers to a type of selective thinking whereby one tends to notice and to look for what confirms one's beliefs, and to ignore, not look for, or undervalue the relevance of what contradicts one's beliefs:- http://www.skepdic.com/confirmbias.html

The reason I started to look more into confirmation bias was due to the following article in Ars Technica - http://arstechnica.com/science/news/2010/07/confirmation-bias-how-to-avoid-it.ars

A good example of this is if you are thinking of buying a new car and all of a sudden you seem to notice lots and lots of the model of the car you was thinking of purchasing. You mind is conditioning itself to notice this make and model of car and making you notice them more, even if there are no more than there was before – you appear to be seeing them everywhere.

Another example is if you start talking to a friend about a certain film and actor and then suddenly notice lots of coincidences, the actor is on a advert, the film is being shown again on TV, a support actor is in another film you just started to watch. The following gives a good example of this. http://youarenotsosmart.com/2010/06/23/confirmation-bias/

If there was no such thing as confirmation bias there would be no conspiracy theories. Conspiracy theories are based upon information which proves the theory correct; those who believe in the theory ignore the evidence that debunks that theory.

So why is there any concern for testers?

Let us start with an example.

You are working closely with the development team and you start to ask them questions about the release you are about to test. You ask their viewpoint on which areas they feel are the most risky and which they feel are the most – so you can adjust your priorities as required, a pretty standard exchange between developers and testers. You now start testing beginning with the area of high risk and work your way to the low risk areas.

You find a few serious bugs in the high risk areas (as expected) and you find no problems in the low risk areas.

After release a major bug is reported in the low risk area you tested. How did you miss the bug? Did you see the bug but your thinking was that everything was working alright? Did confirmation bias play a part? Did your subconscious hide the bug from you? Now this gets very scary, most people who work in software testing know that some bugs try to hide from you, we expect them to hide in the software. What happens if they decide to hide in your brain?

So how can we try and prevent confirmation bias?

The quick and easy way to try and prevent confirmation bias is to ensure that more than one tester tests the same feature, they may bring in their own confirmation bias but hopefully it will be different from the previous testers bias. There is more chance that it will be different if the testers have not discussed the area under test beforehand.

Another way to try and prevent confirmation bias is to do ‘paired testing’ either with a software engineer, another tester or a user. That way you can question each other with regards to what is true and what is false. There is a chance that you could cross contaminate each other with your own confirmation bias, but the risk should be less than if your are working on your own.

It is not easy to remove confirmation bias since it is infectious. The way of working on a software development project requires testers to communicate more and more with other areas of the business and at each stage and with each conversation confirmation bias could be introduced.

So should we lock ourselves away in a dark room with no communication with anyone else on the team? I think I would get out of testing as a career if that happened, the Social Tester (@Rob_Lambert) would now be the anti-social tester, time to get him a ASBO (For our non-UK readers - http://en.wikipedia.org/wiki/Anti-Social_Behaviour_Order)

My view is that there is no realistic way to prevent confirmation bias due to the way software development projects work and that there is a need for everyone to be able to communicate with each other. However if testers are aware that there is such a thing as confirmation bias then they can try and take steps to ensure it does not creep into their testers. That is the whole concept and point of this blog – to help to raise awareness of confirmation bias and how it can effect your testing.