Groups Decision Making: Dum is Over-weighted, Smart is Under-weighted, Of Course

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Take Aways –

  • people tend to overestimate their own performance on hard tasks
  • paradoxically, when given an easy task, they tend to underestimate their own performance (the hard-easy effect)
  • when comparing themselves to others,
  • people with low competence tend to think they are as good as everyone else,
  • whereas people with high competence tend to think they are as bad as everyone else (the Dunning–Kruger effect)

Equality Bias Impairs Collective Decision-Making Across Cultures

Ali Mahmoodi, et al. PNAS March 24, 2015 vol. 112 no. 12 3835-3840

We tend to think that everyone deserves an equal say in a debate. This seemingly innocuous assumption can be damaging when we make decisions together as part of a group. To make optimal decisions, group members should weight their differing opinions according to how competent they are relative to one another; whenever they differ in competence, an equal weighting is suboptimal.

Replicated across three countries (Denmark, Iran, and China), we show that participants assigned nearly equal weights to each other’s opinions regardless of true differences in their competence—even when informed by explicit feedback about their competence gap or under monetary incentives to maximize collective accuracy. This equality bias, whereby people behave as if they are as good or as bad as their partner, is particularly costly for a group when a competence gap separates its members.

A wealth of research suggests that people are poor judges of their own competence—not only when judged in isolation but also when judged relative to others. For example:

  • people tend to overestimate their own performance on hard tasks
  • paradoxically, when given an easy task, they tend to underestimate their own performance (the hard-easy effect)
  • when comparing themselves to others,
  • people with low competence tend to think they are as good as everyone else,
  • whereas people with high competence tend to think they are as bad as everyone else (the Dunning–Kruger effect)

…when presented with expert advice, people tend to insist on their own opinion, even though they would have benefitted from following the advisor’s recommendation (egocentric advice discounting). These findings and similar findings suggest that individual differences in competence may not feature saliently in social interaction.

…When making decisions together, we tend to give everyone an equal chance to voice their opinion. To make the best decisions, however, each opinion must be scaled according to its reliability. Using behavioral experiments and computational modelling, we tested (in Denmark, Iran, and China) the extent to which people follow this latter, normative strategy. We found that people show a strong equality bias: they weight each other’s opinion equally regardless of differences in their reliability, even when this strategy was at odds with explicit feedback or monetary incentives.

worse members of each dyad underweighted their partner’s opinion (i.e., assigned less weight to their partner’s opinion than recommended by the optimal model), whereas the better members of each dyad overweighted their partner’s opinion (i.e., assigned more weight to their partner’s opinion than recommended by the optimal model). Remarkably, dyad members exhibited this “equality bias”— behaving as if they were as good as or as bad as their partner—even when they

  1. received a running score of their own and their partner’s performance,
  2. differed dramatically in terms of their individual performance
  3. had a monetary incentive to assign the appropriate weight to their partner’s opinion.

Recently, psychological phenomena previously believed to be universal have been shown to vary across cultures—where culture is understood as a set of behavioral practices specific to a particular population calling the generalizability of studies based on Western, Educated, Industrialized, Rich, and Democratic (WEIRD) participants into question. To test whether the pattern of advice taking observed here was culture specific, we conducted our experiments in Denmark, China, and Iran. ….

Taken together, the results showed that the more sensitive dyad members had a larger—more positive—influence on the joint decisions. A critical insight, however, came from assessing participants’ confidence in their correct and wrong individual decisions…In particular,

  • the less sensitive dyad members were more likely (compared with their partner) to report high confidence in their incorrect decisions.
  • Conversely, the more sensitive members were more likely (compared with their partner) to report high confidence in their correct
  • the less sensitive dyad members were more likely (than their partner) to lead the group astray by expressing high confidence in their errors;
  • in contrast, the more sensitive dyad members were more likely, compared to their partner, to lead the group to the right answer by expressing high confidence when they were correct

misjudgments of one’s own competence is more severe in individuals with low competence than those with high competence (the Dunning–Kruger effect)…across participants, the absolute difference between the optimal and the empirical weight was negatively correlated with individual sensitivity….In other words, the more sensitive dyad members were better at judging their own competence relative to their partner. The above results can be described as an equality bias for social influence—that is, participants appeared to arbitrate the disagreement trials as if they were as good as or as bad as their partner.

Discussion
An important challenge for group decision-making (e.g., jury voting, managerial boards, medical diagnosis teams) is to take into account individual differences in competence among group members. Although theory tells us that the opinion of each group member should be weighted by its reliability, empirical research cautions that this is easier said than done. To start with – we tend to grossly misestimate our own competence—not only when judged in isolation but also relative to others. This raises the question of whether— and to what extent—people take into account individual differences in competence when they engage in collective decision-making.

  • better-performing group members should (optimally) have followed their partner’s opinion even less often than they actually did
  • Conversely, their poorer-performing counterparts should have followed their partner’s opinion even more often than they actually did
  • Thus, thinking of advice taking as monolithically egocentric may miss out the nuances due to individual differences

Our participants exhibited an equality bias—behaving as if they were as good or as bad as their partner. We excluded a number of alternative explanations…we observed the equality bias across three cultures (Denmark, Iran, and China) that differ widely in terms of their norms for interpersonal trust suggesting that this bias may reflect a general strategy for collective decision-making rather than a culturally specific norm.

… although the better-performing members of each group were more confident, they also overweighted the opinion of their respective partners and vice versa. This suggests that participants may have rescaled their partners’ confidence to their own and made the joint decisions on the basis of these rescaled values.

… an equality bias can be damaging for the group. Indeed, previous research has shown that group performance in the task described here depends critically on how similar group members are in terms of their competence…Previous research suggests that mixed-sex dyads are particularly likely to elicit task-irrelevant sex-stereotypical behavior. We therefore chose to test male participants only.

Our choice leaves open the possibility that such an equality bias may be different in female-only or female-male dyads. However, previous studies have shown that women follow an equality norm more often than men when allocating rewards, suggesting that the equality bias may be found for female dyads too.

Future studies can use our framework to explore the equality bias in male-female and female-female dyads. An important question arising from our approach is the extent to which the model parameters are biologically interpretable at neural level.

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