Estimate alone, then pool

In a group, have everyone make their estimate on their own before anyone hears another. Averaged, independent guesses cancel each other’s errors; guesses that follow the first voice do not.

In 1907 Francis Galton looked at 787 tickets from a contest at a country fair, where each person paid to guess the weight of an ox once it was slaughtered and dressed. The middle guess was 1,207 pounds; the true weight was 1,198. The crowd, taken together, was within 1% of the truth, closer than most of the people in it. This is the wisdom of crowds, and it works best when the guesses are independent: each person’s error is their own, so the errors pull different ways and cancel.

Hearing one voice first spoils it. Amos Tversky and Daniel Kahneman (1974) showed that people’s estimates are pulled towards a number they have just seen, even one they know is arbitrary: anchoring. Jan Lorenz and colleagues (2011) let people see each other’s estimates between rounds; their guesses drew closer together, which made them more confident, but the group’s answer got no more accurate. Later work found that sharing estimates can help when every voice counts equally, but one dominant voice drags the group towards its own error (Becker and colleagues 2017).

Daniel Kahneman, Olivier Sibony and Cass Sunstein, in Noise (2021), call the scatter of judgements that should agree noise, and recommend collecting independent judgements before any discussion. Irving Janis, in his study of groupthink in policy teams (1982), advised leaders not to state their own view at the outset, so that others do not simply line up behind it.

Averaging does not fix everything. If everyone shares the same blind spot, the average shares it too. But for estimates where people err in different directions, one of the cheapest improvements a group can make is to guess alone first, then pool.

Why it matters

Each person’s guess is wrong in its own way, and in an average the errors partly cancel. Once people hear a first number, they lean towards it, so its error is repeated in every guess and survives the average.

Away from the game

Before a meeting that has to estimate a cost, a date or a candidate’s score, ask everyone to write their figure down first, then share them all at once. Hear the most senior person last, not first.