Wisdom of crowds: much ado about nothing

TL;DR

This paper critically examines the 'wisdom of crowds' phenomenon using professional forecast data, finding that crowds rarely outperform individuals and that the supposed collective accuracy is often overstated.

Contribution

It challenges existing explanations for the wisdom of crowds by analyzing real-world forecast data and showing limited collective advantage over individual forecasters.

Findings

Crowds beat all individuals in less than 2% of forecasts.

Crowds beat most individuals in less than 70% of forecasts.

Real-world crowds have only a moderate statistical advantage over individual forecasters.

Abstract

The puzzling idea that the combination of independent estimates of the magnitude of a quantity results in a very accurate prediction, which is superior to any or, at least, to most of the individual estimates is known as the wisdom of crowds. Here we use the Federal Reserve Bank of Philadelphia's Survey of Professional Forecasters database to confront the statistical and psychophysical explanations of this phenomenon. Overall we find that the data do not support any of the proposed explanations of the wisdom of crowds. In particular, we find a positive correlation between the variance (or diversity) of the estimates and the crowd error in disagreement with some interpretations of the diversity prediction theorem. In addition, contra the predictions of the psychophysical augmented quincunx model, we find that the skew of the estimates offers no information about the crowd error. More importantly, we find that the crowd beats all individuals in less than 2% of the forecasts and beats most individuals in less than 70% of the forecasts, which means that there is a sporting chance that an individual selected at random will perform better than the crowd. These results contrast starkly with the performance of non-natural crowds composed of unbiased forecasters which beat most individuals in practically all forecasts. The moderate statistical advantage of a real-world crowd over its members does not justify the ado about its wisdom, which is most likely a product of the selective attention fallacy.