What Is Confirmation Bias?
Confirmation bias is effectively seeing what you want to see. When performing scientific experiments this might mean choosing the results that support your theory and ignoring other or writing them off as experimental error. More subtly, it can refer to setting up an experiment in the way that favours your preferred theory instead of trying to disprove it.
Outside of the lab it can also refer to selectively choosing any form of information and is an occupational hazard of politicians, economists and sociologists amongst others.
It's important to note that confirmation bias doesn't normally mean fraud. The bias is normally entirely subconscious and the victim doesn't realise it.
Confirmation Bias and Divination
Divination, scrying and similar topics are all areas where confirmation bias is a potential problem. This is because they are so hard to control experimentally and because the results are so difficult to interpret.
Let's say I use some divination method - astrology, Tarot reading, crystal ball gazing or whatever - and predict you're going to have good luck soon. Next day you have a small win on the lottery. I might immediately claim "I told you so". But such a claim ignores both the number of other times I've said that to people when it hasn't come true and also all the other predictions I might have made during the reading that didn't come true. More subtly, during the reading both you and I probably thought "good luck" meant something more than a little extra cash - so I've effectively moved the goalposts and retrospectively redefined my prediction to fit the facts.
Dealing With Confirmation Bias
So how do we eliminate the risk of confirmation bias when discussing divination and other similar topics? The simple answer is that we can't.
The very nature of the topic means that we will be making statements and predictions about in "fuzzy" terms. Very few readers claim to be able to predict details such as the role of a dice or the winner of next year's Superbowl. Instead we're usually dealing with complex issues of human nature and society expressed through symbolism.
Some sceptics choose to use this as a reason to dismiss all aspects of divination outright. Whilst it's true that applying traditional scientific method to the field is difficult - if not impossible - I don't think that justifies simply rejecting it.
Perhaps the best we can do is to make sure that we are aware of confirmation bias and its potential impacts, and therefore avoid making excessive claims for success.
That's the approach I've taken. Even allowing for confirmation bias and remembering the statistics I learned for my Maths degree I'm still convinced there's "something" in it.