Document Type


Degree Name

Master of Arts (MA)




Faculty of Science

First Advisor

Roger Buehler

Advisor Role

Thesis Supervisor


Research on the “planning fallacy" shows that people tend to make overly optimistic predictions about the time it will take to complete a task,despite knowing that similar tasks in the past have exceeded predicted completion times. Although the planning fallacy has been well documented in individuals, few researchers have examined how groups make predictions interactively. The main purposes of this thesis are to examine whether people make overly optimistic predictions for group projects and whether group discussion exacerbates this optimistic bias. In three studies, participants were asked to make predictions for an upcoming collaborative task alter engaging in group discussion (discussion condition) or silent thought (no discussion condition). In Study 1, participants overestimated how long it would take to complete a puzzle together in a laboratory setting. A plausible explanation is that inexperience with the task led to this pessimistic bias. In Study 2, participants again completed a puzzle together; however, this time they were given information about previous completion times and a monetary incentive to finish quickly. In Study 3, participants were given an incentive to complete a group take-home assignment. In addition, half of the participants in Studies 2 and 3 made an initial, private prediction prior to the group discussion manipulation. In both of these studies, participants tended to underestimate how long the task would take, and group discussion led to more optimistic predictions. Overall, the results of these studies suggest that group discussion may ofien heighten rather than attenuate optimistic biases in task prediction.

Convocation Year


Convocation Season