HPC › Decisions › Glossary
Anchoring Bias is a cognitive heuristic in which an initial piece of information, the anchor, exerts a disproportionate pull on subsequent judgements and decisions. Even demonstrably arbitrary or irrelevant anchors shift numerical estimates measurably because people adjust insufficiently from the starting point, leaving final judgements skewed towards whichever figure they encountered first.
The phenomenon is also called the anchor effect or anchoring effect; the core mechanism is identical regardless of whether the anchor originates externally or is self-generated.
How it works
Tversky and Kahneman established anchoring bias through a deceptively simple experiment: participants who watched a spinning wheel land on 65 gave higher estimates for unrelated quantities than those who saw it stop at 10, confirming that even a demonstrably random number reshapes subsequent judgement 1. The primary mechanism is insufficient adjustment. When forming an estimate, people begin from the anchor value and shift along a mental scale until they reach a plausible stopping point; because adjustment is cognitively effortful, they halt at the first acceptable figure rather than continuing to the statistically optimal one 2.
A complementary mechanism, selective accessibility, operates in parallel. When someone treats the anchor as a candidate answer, that act activates semantically consistent information in memory; knowledge aligned with the anchor becomes more retrievable, biasing the evidence base from which the final judgement is assembled 3. The two processes work in concert: fast, automatic knowledge activation and slower, deliberate adjustment both contribute, often simultaneously, which is why anchoring effects persist even when decision-makers are aware of them 2.
Example
A hiring manager reviews a candidate's salary expectation of £90,000 before any offer is discussed. Although the manager had independently valued the role at £75,000, the negotiation gravitates towards the candidate's figure, and the final offer settles at £83,000. Had the candidate opened with £70,000, the same manager would likely have anchored lower and reached a different conclusion, without any awareness of the influence at work.
The candidate who named a number first did not merely open a negotiation; they set the gravitational centre around which all subsequent adjustments would orbit.
Why it matters
The practical reach of anchoring bias extends well beyond the laboratory. Across negotiation, legal sentencing, property valuation, and salary setting, first-offer effects account for a substantial portion of variance in final outcomes, conferring a structural advantage on whichever party names a figure first 3. In clinical medicine, the consequences are more serious still. A large-scale study of emergency patients presenting with congestive heart failure found that physicians anchored to the presenting diagnosis and were significantly less likely to order pulmonary embolism workup when the visit reason explicitly named CHF, showing that anchoring can foreclose life-critical investigations 4.
A further complication is that awareness of the bias provides limited protection against it. The adjustment process terminates at the first plausible value whether or not the decision-maker knows about anchoring. Structured protocols, pre-committed evaluation criteria, and deliberate consider-the-opposite exercises, in which a person generates reasons the anchor might be wrong before settling on an estimate, produce more reliable debiasing than knowledge alone 2.
What is an example of anchoring bias in everyday life?+
Retail pricing is the most visible application. A product listed at 'was £200, now £120' installs £200 as an anchor, making the discounted figure feel like a bargain regardless of genuine market value. The same mechanism operates in property asking prices, restaurant menus, and any context where a reference price precedes a transaction price {{cite:10.1016/j.socec.2010.10.008}}.
How does anchoring bias affect salary negotiation?+
Whoever names a salary figure first sets the anchor around which all subsequent discussion is organised. The first-offer effect means the party who opens with a higher number typically achieves a more favourable final outcome; first-offer effects can account for more than half the variance in negotiated prices {{cite:10.1016/j.socec.2010.10.008}}.
Can you reduce or overcome anchoring bias?+
Complete elimination is not achievable, but the magnitude can be reduced. Consider-the-opposite instructions, where decision-makers actively generate reasons the anchor might be wrong before settling on an estimate, consistently lower anchoring effects in controlled settings. Structured decision protocols with pre-set evaluation criteria perform more reliably than simply being aware of the bias {{cite:10.1111/j.1467-9280.2006.01704.x}}.
Does anchoring bias affect medical diagnosis?+
Clinical evidence indicates it does. A study of over 100,000 emergency visits found that physicians were significantly less likely to order pulmonary embolism investigations when a patient's visit was logged as congestive heart failure, suggesting the presenting diagnosis anchored clinical attention away from alternative possibilities {{cite:10.1001/jamainternmed.2023.2366}}.
