LETTER

LETTER

Solving problems in social groups Jeroen Bruggemana,1

Humans live and work in groups where they face similar, and often shared, problems, ranging from finding resources to avoiding external threats. To solve a problem at hand, they have to make sense of it and develop an accurate idea of a solution. The wisdom of crowds means that the average of a variety of inaccurate ideas, arrived at independently, is often very accurate, whereas social influence results in convergence to a single inaccurate idea, called groupthink. Interestingly, Becker et al. (1) show that if people interact, rather than think independently, both individuals’ ideas and the group’s consensus can become more accurate—provided that knowledgeable individuals are more self-confident than others, as in animal groups (2). However, human self-confidence tends to be noisy, with self-deceivers among the self-confident (3). Are we bound to be stuck in groupthink after all? This problem can be overcome if individuals know their group members’ expertise and adjust their ties or tie strengths accordingly. Because reputations of expertise are based on others’ judgments, they tend to be less biased than self-judged expertise. For the duration of the current problem, individuals then shift their strongest ties to the most knowledgeable group members,

by whom they will be more strongly influenced (4). In the group network, weighted ties 0 ≤ wij ≤ 1 connecting i to j are in a row-stochastic adjacency matrix, and hence increasing tie strength here implies reducing tie strength there. Because the ideas of communicating individuals approach each other (1, 5, 6), and thus pairwise differences between ideas xj and xi decrease, an individual’s change of opinion between t0 and t1 can be written as (6) xi ðt1 Þ − xi ðt0 Þ = si

X

  wij xj ðt0 Þ − xi ðt0 Þ ,

[1]

i≠j

where 0 ≤ si ≤ 1 is i’s susceptibility to social influence by the group as a whole, and 1 − si indicates self-confidence. It can now be easily seen, or calculated, that if individuals’ tie strengths correlate with their alters’ reputations or expertise correlates with 1 − si, both individual and group outcomes are better than those of independent individuals. The wisdom of crowds is best when both hold true, and there is an availability of diverse expertise in various problems that a group may encounter (7).

1 Becker J, Brackbill D, Centola D (2017) Network dynamics of social influence in the wisdom of crowds. Proc Natl Acad Sci USA 114:E5070–E5076. 2 Couzin ID, Krause J, Franks NR, Levin SA (2005) Effective leadership and decision-making in animal groups on the move. Nature 433:513–516. 3 Robert Trivers R (2011) Deceit and Self-Deception: Fool Yourself the Better to Fool Others (Allen Lane, London). 4 Bruggeman J (2016) The strength of varying tie strength. Am J Sociol 121:1919–1930. 5 Takacs ´ K, Flache A, Mäs M (2016) Discrepancy and disliking do not induce negative opinion shifts. PLoS One 11:e0157948. 6 Friedkin NE, Johnsen EC (2011) Social Influence Network Theory: A Sociological Examination of Small Group Dynamics (Cambridge Univ Press, Cambridge, UK). 7 Page S (2007) The Difference: How the Power of Diversity Creates Better Groups, Firms, Schools, and Societies (Princeton Univ Press, Princeton).

a Department of Sociology, University of Amsterdam, 1018 WV Amsterdam, The Netherlands Author contributions: J.B. wrote the paper. The author declares no conflict of interest. Published under the PNAS license. 1 Email: [email protected].

www.pnas.org/cgi/doi/10.1073/pnas.1713474114

PNAS | October 31, 2017 | vol. 114 | no. 44 | E9183