Confirmation bias
From RationalWiki
A confirmation bias is the tendency for people to seek out information that conforms to their pre-existing view points and to ignore information that goes against them. It is a type of cognitive bias and a form of selection bias toward confirmation of the hypothesis under study. Confirmation bias is also important in science in general.
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[edit] We all do it...
Confirmation bias is one of the traits that just comes with the human condition, and the scientific method has basically "evolved" to try and counteract it. There is a tendency to test predictions of ones hypothesis that confirm it rather than seeking predictions that would disconfirm a hypothesis. Oftentimes disconfirmation is a more practical and obvious method to test between hypothesis but even practicing scientist often miss these examples.
[edit] Wason card problem
The Wason Card problem highlights confirmation bias quite nicely. In the problem, four cards are presented, each labeled in some manner, usually two with letters and two with numbers (A, B, 1, 2) and each card also has a corresponding figure on the back - each card has a letter and a number on opposite sides. The hypothesis is then tested; "If a card has a vowel on one side, then it has an even number on the other side." The aim of the experiment is to test the hypothesis by turning as few cards as possible.
Most people, when given the problem will turn over the even number (2) and the vowel (A) to see what is on the other side. This is instinctive because turning these two cards and observing another vowel and an even number respectively would confirm the hypothesis - and without context or applied critical thinking, this will be people's normal approach. However, to fully confirm the hypothesis, a third card would be needed to be flipped; 1, to confirm that it doesn't have a vowel on the other side, thus disproving the hypothesis.
[edit] Solution
If one sets out to disprove the hypothesis the problem can be solved in two turns, rather than three. The correct cards to turn over would be 1 and A. First, turning over the odd number and viewing a vowel on the other side of that card would invalidate the hypothesis quickly and more efficiently as it states the vowels don't have odd numbers on the back. This is the main counter-intuitive step that demonstrates the need to try and disprove a hypothesis. Once the odd numbered card is flipped, the next logical card to turn would then be A to confirm whether it had an even number. The B and 2 cards are actually irrelevant to proving or disproving the hypothesis. The hypothesis states nothing about what is on the back of a consonant card (B) so it is totally irrelevant and uninteresting to test it. Revealing the opposite side of 2 would either confirm the hypothesis, by displaying a vowel, or say nothing, by showing a consonant (which is the same reason that the B card is uninteresting and irrelevant).[1]
[edit] In ID
A prime example stems from the intelligent design and creationism movements. Proponents of these ideas start by assuming that an intelligent creator must have been behind life (often assuming the Christian god) and then seeking out any evidence that might back up this claim. For example, Answers in Genesis often claims that fossils in the ground are proof of a Global flood and that layering is caused by the relative abilities of animals to reach higher grounds. They quote such examples as humans and primates being on top of dinosaurs because we could climb to higher points on the landscape. However, they never address an evidence that might disconfirm this hypothesis such as why angiosperm plants and their pollen is never found below vascular fern fossils. Such examples are best explained by common descent and are thus ignored through confirmation bias by creationist.
