Angela Hung

Angela Hung is an economist whose work with Charles Plott tested how the rules of a decision-making exercise affect whether a group can use its members’ private information. Their marble-drawing experiment showed that a sequential group could often fall into an information cascade, but that changing the reward to depend on the group’s majority answer led participants to attend more to their own evidence and made the collective judgment more accurate.

The Marble Experiment

Hung and Plott designed a classroom experiment around two urns. Urn A contained twice as many light marbles as dark ones, while Urn B contained twice as many dark marbles as light ones. The experimenters selected one urn, and volunteers drew marbles from it in sequence. Each participant had to identify which urn was in use; a correct answer initially earned a couple of dollars.

Participants had two sources of information: the color of the marble they themselves drew and the guesses announced by people who had drawn before them. The marble was private information; participants could not disclose its color, only their conclusion about the urn. This created a conflict between personal evidence and the apparent direction of the group. A participant who drew a light marble might have reason to favor Urn A even after hearing several earlier participants choose Urn B.

From Individual Incentives to Group Accuracy

Under the original rules, most participants in that situation chose Urn B, following the preceding guesses rather than their own contrary draw. Information cascades began in 78 percent of the trials. The experiment thus made visible a weakness in sequential decisions: later participants could mistake earlier choices for independent evidence, even when those choices had themselves been shaped by the group.

Hung and Plott then changed what counted as success. Participants still drew marbles and made their choices in order, but payment now depended on whether the group’s collective answer, determined by majority vote, was correct. The objective shifted from maximizing each person’s individual chance of being right to helping the group reach the right answer.

That change encouraged participants to give greater weight to their own marble and less to the choices they had already observed. A private draw was imperfect evidence, so relying on it could make an individual guess less likely to be correct. Yet the group benefited because its decisions incorporated more distinct information instead of allowing early choices to dominate. With collective accuracy at stake, the group’s judgment became significantly more accurate than the judgment of groups subject to cascading decisions.

Significance for Collective Decisions

The experiment reduced the influence of the sequential order without removing it: participants still decided one after another, but the new incentive made previous choices less important to them. Hung and Plott’s results therefore distinguished individual accuracy from collective accuracy. A decision that is not the best response for a participant seeking to be right alone can still help the group by preserving a piece of information that would otherwise disappear.

The broader implication drawn from the experiment is that organizations can improve group judgment by asking people to offer their views simultaneously, or as nearly simultaneously as possible, rather than letting early opinions set the course for those who follow. The exercise also illustrates the value of independence: a group can aggregate useful information only when its members do not simply substitute other people’s conclusions for their own evidence.