Before a meeting, a CEO asks each executive to email their independent assessment of a project. During the meeting, she reveals the assessments. If instead she'd asked for opinions around the table, the first speaker's view would have anchored everyone else's — and the "group wisdom" would have been one person's opinion, repeated six times.
The Framework
Decorrelating errors is Kahneman's principle that the wisdom of a group depends entirely on the independence of its members' judgments. When judgments are independent (each person forms their opinion without knowing others' opinions), errors tend to cancel out — some overestimate, some underestimate, and the average is more accurate than any individual. But when judgments are correlated (each person is influenced by what others have said), errors compound instead of canceling. The group converges on the first opinion expressed, and the "collective wisdom" is actually one person's bias amplified by social proof.
The practical prescription is simple: collect independent judgments before group discussion. Written assessments, sealed bids, or simultaneous reveals prevent the cascade of social influence that destroys the value of aggregation. The order of speaking in a meeting is not a trivial logistical detail — it determines whether the meeting produces wisdom or conformity.
Where It Comes From
Kahneman presents decorrelating errors in Chapter 7 of Thinking, Fast and Slow alongside his discussion of WYSIATI and the halo effect. The concept draws on the mathematical foundations of aggregation (the "miracle of aggregation" requires independent errors) and on research showing that group discussions typically reduce rather than increase judgment accuracy. The principle is related to James Surowiecki's Wisdom of Crowds thesis — which explicitly requires independence as one of its four conditions.
> "The standard practice of open discussion gives too much weight to the opinions of those who speak early and assertively, reducing the quality of the group's decision." — Thinking, Fast and Slow, Ch 7
Cross-Library Connections
Fisher's brainstorming protocol in Getting to Yes — separate inventing from deciding — implements decorrelation: during brainstorming, no evaluation occurs, preventing early ideas from anchoring the group.
Kahneman's structured interview protocol (Ch 21) is decorrelation applied to hiring: scoring each trait independently before forming a global impression prevents the halo effect from correlating all scores with the first impression.
The Implementation Playbook
Meetings: Before any group discussion of a strategic question, ask each participant to write their assessment independently — in writing, submitted before the meeting. Present all assessments simultaneously. Then discuss. The independence of the initial assessments ensures that errors are decorrelated, and the subsequent discussion can build on genuine diversity of perspective rather than anchored conformity.
Hiring Panels: Each interviewer should score the candidate independently before the panel discussion. If the panel discusses first and then scores, the most senior or assertive interviewer's assessment will anchor all others.
Investment Committees: Each analyst should submit their valuation independently before the committee meeting. Committee discussions that start with a senior analyst's view produce anchored conformity, not collective wisdom.
Brainstorming: Brainwriting (silent individual idea generation) before brainstorming (group discussion) produces more and better ideas, because the initial independence prevents the first idea from anchoring the group.
Key Takeaway
The wisdom of groups is real — but only when individual judgments are independent. The moment one person's opinion influences another's, the aggregation loses its mathematical advantage. The prescription: always collect individual judgments before group discussion. It takes 5 extra minutes and prevents every meeting from degenerating into an anchoring exercise.
Continue Exploring
[[Anchoring (Dual Mechanism)]] — The mechanism by which early opinions contaminate later judgments
[[WYSIATI]] — Each person's independent WYSIATI is different; aggregation captures more "all there is"
[[Confirmation Bias]] — Once group consensus forms, the group seeks confirming evidence
📚 From Thinking, Fast and Slow by Daniel Kahneman — Get the book