Confirmation bias is the tendency to search for, favour, interpret, and recall information in a way that confirms beliefs we already hold — while giving less weight to evidence that challenges them. It is one of the most widely studied cognitive biases and one of the most consequential, because it affects not just casual opinion but scientific research, financial decisions, medical diagnoses, and political judgement.

The term was popularised by English psychologist Peter Wason, whose 1960 card-selection experiment demonstrated that people prefer evidence that confirms a hypothesis to evidence that could refute it. Subjects were given a sequence of numbers and asked to discover the underlying rule. Most participants tested only examples that confirmed their initial guess, rarely attempting sequences that could prove it wrong. The confirmation was comfortable; the disconfirmation was avoided.

How Confirmation Bias Works

Confirmation bias operates through several distinct mechanisms:

• Selective search. When researching a question, we tend to seek out sources and arguments that support our current view. Someone who believes a particular health remedy works will search for studies confirming its efficacy; evidence against it simply does not get searched for.
• Biased interpretation. The same evidence can be interpreted differently depending on what we already believe. A rising stock price confirms the investment thesis of the buyer and is dismissed as a "dead cat bounce" by the sceptic who shorted it.
• Selective recall. We remember information that supports our beliefs more readily than information that challenges them. A manager convinced an employee is underperforming will remember mistakes vividly and forget instances of good work.

Why Confirmation Bias Is Hard to Overcome

Confirmation bias is especially persistent for two reasons. First, it is reinforced by social environments: we tend to associate with people who share our views, read media that reflects our worldview, and share content that confirms our beliefs. The digital information environment has made this dramatically worse, curating feeds to show us exactly what we already agree with.

Second, the bias feels like good epistemics from the inside. When you find evidence consistent with your belief, it feels like rational confirmation. It takes active effort to notice what you are not looking for.

Confirmation Bias in Practice

The bias appears across almost every domain:

• Investing: A trader who has taken a position in a stock unconsciously seeks out bullish news and dismisses bearish analysis, even when the bearish case is stronger.
• Medicine: A physician who has made an initial diagnosis may order tests that confirm it and downplay symptoms that suggest an alternative, a pattern known as anchoring in diagnostic medicine.
• Politics: Voters evaluate the same policy statement differently depending on which party proposed it. The content matters less than the tribal source.
• Relationships: Once we decide we like or dislike someone, we interpret their behaviour through that lens. The same lateness is forgivable from a friend and a character flaw in someone we distrust.

How to Counteract Confirmation Bias

No technique eliminates confirmation bias entirely, but several reduce its impact:

• Actively seek disconfirming evidence. For any belief you hold, ask: "What would I need to see to change my mind?" Then deliberately look for that evidence.
• Consider the opposite. Before committing to a conclusion, spend time genuinely constructing the strongest case against it. This is known as a pre-mortem in decision analysis.
• Diversify your sources. Read perspectives that challenge your own, not to capitulate to them, but to understand where the strongest counterarguments lie.
• Separate hypothesis formation from hypothesis testing. Decide in advance what evidence would confirm or disconfirm a belief, before looking at any data.

Practise Spotting It

Confirmation bias is a recurring theme in scenarios throughout the Dojo. Encountering it across different contexts — investment decisions, relationship dynamics, workplace scenarios — builds the pattern recognition that makes it catchable in real life. The Library entry also links this bias to related distortions like the Texas Sharpshooter fallacy and Availability Heuristic.