Anchoring effect

The anchoring effect occurs when people consider a value for an unknown quantity before estimating that quantity. The estimates of the quantity are found to stay close to the number that people considered (Kahneman 2011).

Anchoring is a well-proven effect in experimental psychology. Experiments included Kahneman & Tversky rigging a wheel of fortune wheel numbered 0 to 100. The wheel was rigged so that when spun it would always land on either 10 or 65. Students were asked to spin the wheel and write down their predetermined number before being asked two questions. The questions the students asked were;

Is the percentage of African nations among UN members larger or smaller than the number you wrote?

What is your best guess of the percentage of African nations in the UN?

Now for the students, the wheel was perceived to be random chance so logically should have no impact on their answer, however, the average estimates of those who saw 10 and 65 were 25% and 45%, respectively.

The process of the anchoring effect is believed to be a bias that occurs in part due to adjustment error. In this case, the brain has been given a starting point (anchor) and now adjusts from that anchor until it reaches an answer it believes to be correct. These adjustments are often inaccurate as people stop adjusting when they are no longer confident in moving away from the anchor. Another process is that the anchor has a priming effect where memories associated with the anchor are activated, and our estimate is then significantly influenced by a conjured-up image of the anchor.   

Anchoring has a tremendous impact on our daily life including how we negotiate house prices when limits are placed on food items when parents are arranging a bedtime with their children when negotiating a salary etc.

As the anchoring effect is an automatic response most of the time the best defence, we have against this bias is to think the opposite. This means thinking of evidence against the initial anchoring value.


Kahneman, D. (2015). Thinking, fast and slow. New York: Farrar, Straus and Giroux.