Groups are more accurate than individuals

I just read "Psychology: The crowd within" in the June 26th edition of The Economist. Statisticians have recognized for more than a century that the average of a number of independent measurements of a value are expected to be a more accurate estimate of that value than a single estimate. Psychologists have observed for a century the odd fact that similarly aggregating a large number of guesses of a quantity (such as the weight of a pig seen at a county fair) will be more be more accurate than the average individual person's guess.

The Economist describes a new research result as follows:

The two researchers asked 428 people eight questions drawn from the “CIA World Factbook”: for example, “What percentage of the world’s airports are in the USA?” Half the participants were unexpectedly asked to make a second, different guess immediately after they completed the initial questionnaire. The other half were asked to make a second guess three weeks later.

Dr Vul and Dr Pashler found that in both circumstances the average of the two guesses was better than either guess on its own. They also noticed that the interval between the first and second guesses determined how accurate that average was. Second guesses made immediately improved accuracy by an average of 6.5%; those made after three weeks improved the accuracy by 16%.

Even after three weeks, the result is still only one-third as good as the wisdom of several different people. But that this happens at all raises questions about “individuality” within an individual. If guesses can shift almost at random, where are they coming from?

Comment: This suggests that the social construction of knowledge is important in a very deep way. Of course it seems obvious that when people can discuss an issue, comparing and reviewing the quality of data and analyses, they may be expected (under the right circumstances) to come to better communal understanding of that issue than they might be leaving it to individual unaided judgments. So too, in a community in which many individuals independently try different ways of doing the same thing, observation of which ones have success will lead to the diffusion of successful innovations. This research, however, suggests that people may see things better collectively (or repetitively) than individually. JAD