Confirmation Bias
What is Confirmation Bias?
Confirmation bias is the tendency to seek, notice and remember evidence that supports what you already believe, while discounting evidence that does not.
A belief you already hold changes how you handle information at three stages: which sources you go to, how you read what you find, and what you later recall. Evidence that fits gets accepted at face value, while evidence that conflicts gets picked apart for flaws. Because the filter is directional, gathering more information can leave two people further apart rather than closer together. In economics it helps explain why forecasters cling to a prediction after the data turns, and why investors hold a losing position by reading every bad quarter as temporary. Note the contrast with the availability heuristic: availability distorts a judgment through what is easy to remember, with no prior conclusion required, while confirmation bias needs a conclusion to defend.
Confirmation Bias: a worked example
A trader is convinced a stock will rise and follows 20 analyst notes on it. Twelve are positive and eight are negative. He reads all 12 positive notes fully, spending an average of 6 minutes on each, and skims the 8 negative ones for about 1 minute each. That is 12 × 6 = 72 minutes on supporting evidence against 8 × 1 = 8 minutes on the rest, so 90 percent of his reading time went to one side of a 60-40 split in the underlying research. He then reports that the analysts are overwhelmingly bullish.
The mistake students make with confirmation bias
Students usually describe confirmation bias as lying or refusing to look at the other side. The people it describes typically do look, and they believe they are being fair; the filtering happens in how carefully each piece gets checked. A second slip is treating it as a problem of too little information. Adding information can make it worse, because a bigger pile gives a motivated reader more to select from.
Confirmation Bias questions
How is confirmation bias different from the availability heuristic?
Confirmation bias is driven by a belief you are protecting, while the availability heuristic is driven by how easily an example comes to mind. Someone with no view at all can still misjudge a risk through availability, but confirmation bias cannot start without a prior conclusion. One filters evidence for and against a position; the other substitutes memory for frequency.
Why does confirmation bias matter in economics?
Confirmation bias matters in economics because it keeps wrong forecasts and bad positions alive after the evidence has turned. Traders hold losers, firms stick with failing strategies, and policymakers defend a model past the point where data supports it. It also undercuts the standard assumption that people update their beliefs correctly when new information arrives.
Can you avoid confirmation bias?
You cannot switch confirmation bias off, but you can build procedures that force disconfirming evidence in front of you. Writing down in advance what result would change your mind, asking someone to argue the other side, and setting rules that trigger automatically all limit the damage. These work by removing the choice of what to look at, rather than by trying harder to be fair.
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