Anchoring Bias

Anchoring bias is the tendency for a person's judgments or estimates to be influenced by an initial reference point, or anchor, even when that anchor is arbitrary or irrelevant to the actual question at hand. The concept originated in psychophysics research on how an initial stimulus in a sequence serves as a comparison point for later stimuli, and the psychologists Amos Tversky and Daniel Kahneman formally developed anchoring as a general heuristic for making estimates under uncertainty in their influential 1974 work on judgment. Anchoring effects have been documented for both numeric estimates, such as a price, and for physical judgments of quantities like length or weight; a commonly cited real-world example is that shoppers are more likely to buy a car when it is displayed next to a more expensive model that serves as an anchor. The behavioral economist Dan Ariely later showed the effect can be induced by wholly arbitrary numbers, such as the last digits of a person's own social security number, which shifted how much people were willing to bid for unfamiliar items by 60 to 120 percent, and the bias has proven strikingly resistant to correction, persisting even when people are explicitly warned about it or offered a monetary incentive to avoid it.