This research investigated the effects of aggregation level on decision-making performance and confidence. The study made use of experienced territory managers as subjects. As part of their regular job responsibilities, they had all carried out a task closely resembling the one in this experiment. The research sought to identify patterns of decision-making suggesting that individual differences play an important role. With an average of 6.8 years of experience, 104 territory managers in a manufacturing firm planned the coming year's product distribution. Each manager received reports for two hypothetical territories that differed in their level of aggregation. Confidence in their plans was related to experience and to decision-making style, but not to preference. Decision-makers almost always preferred detailed data, while summary data appeared to better serve heuristic planners and detailed data better served analytic planners.