Anchoring
How an initial number — even an arbitrary one — pulls later numerical judgments toward itself, and why expertise barely helps.
Anchoring is the tendency for an initial number — the anchor — to pull later numerical judgments toward itself, even when the anchor is arbitrary, implausible, or explicitly labeled irrelevant. Tversky and Kahneman demonstrated the effect in 1974 with a rigged wheel of fortune: after watching the wheel land on 10 or 65, subjects estimated the percentage of African nations in the United Nations. Median estimates moved from 25 to 45 depending on the spin, though the wheel carried no information at all.
Two mechanisms produce the effect. Selective activation: entertaining a number makes anchor-consistent knowledge more accessible, so evidence gets read in the anchor's shadow. Insufficient adjustment: people start at the anchor and adjust toward their true estimate, but adjustment stops too early, especially under time pressure or cognitive load. The two routes matter because they respond differently to conditions — knowledge-based anchors distort interpretation, while pure-number anchors distort the starting point of the search.
The effect survives expertise and real stakes. Northcraft and Neale (1987) found that professional real-estate appraisers' valuations shifted with the listing price they were shown. Englich, Mussweiler, and Strack (2006) found that experienced judges recommended longer sentences when the prosecutor's demand was higher — even when the demand was determined by a dice roll. In negotiation, the first offer predicts the final settlement better than objective value does, which is why the party who moves first often wins. In retail, an inflated "regular" price makes the sale price feel like a gain; in fundraising, a suggested donation line raises average gifts.
Anchoring is among the most robust effects in behavioral research, but its size varies: it shrinks when people hold strong, well-calibrated knowledge of the quantity, and some large-scale replications find weaker effects than the originals. The practical defense is procedural, not intellectual — generate your own estimate before hearing anyone else's number, and treat the first number on the table, in salary talks or budgets or price tags, as a position to argue from rather than a fact about value. Together with loss aversion, anchoring explains why sellers frame numbers the way they do: the frame sets the reference point before the judgment begins.
Tags
behavioral economics decision making heuristics psychology