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PLoS One. 2018 Sep 24;13(9):e0204462. doi: 10.1371/journal.pone.0204462. eCollection 2018.

Adolescents show collective intelligence which can be driven by a geometric mean rule of thumb.

Author information

School of Biological Sciences, University of Bristol, Bristol, United Kingdom.
Instituto Cajal, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
Champalimaud Research, Champalimaud Center for the Unknown, Lisbon, Portugal.
Department of Psychology, University of Bath, Bath, United Kingdom.


How effective groups are in making decisions is a long-standing question in studying human and animal behaviour. Despite the limited social and cognitive abilities of younger people, skills which are often required for collective intelligence, studies of group performance have been limited to adults. Using a simple task of estimating the number of sweets in jars, we show in two experiments that adolescents at least as young as 11 years old improve their estimation accuracy after a period of group discussion, demonstrating collective intelligence. Although this effect was robust to the overall distribution of initial estimates, when the task generated positively skewed estimates, the geometric mean of initial estimates gave the best fit to the data compared to other tested aggregation rules. A geometric mean heuristic in consensus decision making is also likely to apply to adults, as it provides a robust and well-performing rule for aggregating different opinions. The geometric mean rule is likely to be based on an intuitive logarithmic-like number representation, and our study suggests that this mental number scaling may be beneficial in collective decisions.

Conflict of interest statement

The authors have declared that no competing interests exist.

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