Confirmation bias, according to Wikipedia is

a tendency of people to favor information that confirms their beliefs or hypotheses. People display this bias when they gather or remember information selectively, or when they interpret it in a biased way. The effect is stronger for emotionally charged issues and for deeply entrenched beliefs.

It’s just one kind of bias.  If you look of types of bias on the inner webs you’ll find lots of them.  It’s any sort of preconceived approach to anything that will keep you from discovering what’s really true.  Scientists know that they have biases.  They may not be aware of what biases they bring into an experiment, but they know that those bias have to potential to influence the results of their experiment.  Science, particularly medical science, has created double blind experiments that have as their goal, to remove, so much as is possible, bias from their results so that there is a better chance of discovering the truth.

As humans we are biased.  And one of the most widely shared (I’d say universally shared) biases is confirmation bias.  When I look out at the world I find evidence wherever I look that confirms what I already know.  I don’t see much that says I’m wrong.  In fact, I hardly every see evidence that I’m wrong.  But I know from long experience that I’m often wrong.  So I know something is going on that is clouding my interpretation of the world. And a big part of that is confirmation bias.  I think it’s something we all share.

I recently had a conversation with a friend.  He told me about a friend of his who can travel in time.  She can go forward to see what’s going to happen and then come back and tell people about it.  He said that from time to time she’d go to Las Vegas, travel in time to find out what numbers or cards were going to come up and then travel back to bet on them.  That’s how she made some extra pocket money.  I responded to his description with what I thought was humorous and appropriate skepticism.  I assumed that a claim like that would be treated skeptically by pretty much everyone.

Later my friend told me he was taken aback by my skepticism and felt angry.  He felt that I’d called him and his friend a liar.  It hadn’t occurred to me that either of them had been lying, but I could understand his reaction.  He told me that his friend traveling in time was completely consistent with his word view and since his friend said that was what was happening, he believed it.

My take on the situation is this.  While it’s possible that the time-traveller is lying, I tend to doubt it.  I suspect that she has experiences.  At one point she decided that those experiences were time travel.  And after that she found lots of evidence that that was what was going on, and saw virtually none that suggested she was wrong.  Over time confirmation bias was sufficient to make this a truth for her.  She told other people about it.  They started coming to her for advice and she built a business out of being a time traveller.  I hear this story as being one about a psychic, but a psychic who gives her story a bit of a twist.  I’m sure both she and her clients have unlimited evidence that she really can time travel.  Confirmation bias is extremely powerful.

While I don’t know what this woman says to her clients the usual routine of a psychic is to make many, many observations and many, many predictions.  A combination of basic intuition, experience and an understanding of people just about guarantees that some of the observations or predictions will hit the mark.  The client will then tend to remember the hits and forget the misses.  When you only remember the hits, the results can seem very powerful.  Confirmation bias is at work for both the psychic and her client.

So I never intended to accuse anyone of lying.  But my assumption is that no one can time travel and there aren’t any real psychics.  That’s the position I start from.  So I’m going to find lots of evidence that the claims of a psychic aren’t true and that people can’t time travel.  I will find evidence for my own prior beliefs and virtually no contradictory evidence.

At this point is sounds like we’re at an impasse.  One person will believe something and find lots of evidence for it.  The other person does not believe that thing and will find lots of evidence against it.  If that was all we had to work with we’d have a world that looks a lot like the world we currently live in.  But there are ways around this.  That are ways to test claims that are independent of confirmation bias.  The entire scientific method has been designed as a way to gather knowledge that is as independent of bias as possible.

No matter what rules of science, logic or reason are employed to find out what’s so, there will always be people who will ignore the finding because it doesn’t fit into their confirmation bias.  That’s just the way it is.  But it’s worth acknowledging that we’re all biased and that it’s worth attempting to get past that in an effort to get just a bit closer to what is really true.