What Is the Anchoring Effect?
The anchoring effect is one of the most powerful and pervasive cognitive biases. First demonstrated by Amos Tversky and Daniel Kahneman in 1974, it describes how an initial piece of information — the anchor — disproportionately influences subsequent judgments, even when the anchor is completely arbitrary.
The Classic Experiment
In Tversky and Kahneman's original study, participants spun a rigged wheel of fortune that landed on either 10 or 65. They were then asked whether the percentage of African countries in the United Nations was higher or lower than that number, and then to estimate the actual percentage. Those who saw 65 estimated an average of 45%, while those who saw 10 estimated only 25% — a massive difference driven by a clearly random number.
Anchoring-and-Adjustment Model
This simulator implements the anchoring-and-adjustment model: each person starts from the anchor and adjusts toward what they believe is the correct answer, but the adjustment is insufficient. The adjustment factor α controls how far people move — with α = 0.4, people only travel 40% of the distance from anchor to truth. The noise parameter adds realistic individual variation around this biased mean.
Reading the Visualization
The top histogram shows the distribution of estimates in the population. The red dashed line marks the true value, the cyan line marks the anchor, and the white line marks the mean estimate. The gap between the true value and the mean estimate is the anchoring bias. The bottom scatter plot shows individual estimates, revealing both the central tendency toward the biased mean and the spread of individual variation. Try moving the anchor dramatically — notice how the entire distribution shifts, even though the true value hasn't changed.