Are two heads better than one?

In theory, yes. In practice, no.

When we make decisions in groups we tend to discuss and debate shared information rather than offer private information (information that select members of a group hold).

Why do we prefer shared information?

  • Information usage is a disjunctive task: the group can use a piece of information as long as at least one member mentions it in the group discussion. Therefore, the probability of shared information being mentioned is higher than that of unshared information.
  • Karau and Kelly (1992) propose that information exchange is costly, both cognitively, socially, and in terms of time taken. Therefore, shared information is that which dominates in group processes.
  • Wittenbaum et al. (1999) contend that members prefer to “discuss and repeat information known by all members (shared) more than they do information known by one member (unshared).” Doing so enhances one's own credibility and reduces dissonance. A twist on this is that members who might have valuable unshared information tend to accept a powerful other member, even if acceptance does not fully use the unshared information.

How can you mitigate the shared information bias?

  • Ranking. Hollingshead (1996) finds that asking members to rank all alternatives instead of getting them to decide on the one best alternative also reduces bias.
  • …having some members as experts (who know the characteristics of hypothetical candidates for student government) and knowing which members are indeed experts. …bias from common knowledge effect is reduced by knowing which members are experts, but not by just having experts in the group.
  • In a related experiment, Larson et al. (1998) find that team leaders help reduce the bias from the common knowledge effect by repeating and eliciting unshared information. However, because they also do the same for shared information, the accuracy of group work (the medical diagnosis in the experimental setting) is not improved.

Follow the Farnam Street Blog via TwitterEmail, or RSS.

Shop at and support Farnam Street