A comparison of strategies for reducing interval overconfidence in group judgments.

The present experiments examined several strategies designed to reduce interval overconfidence in group judgments. Results consistently indicated that 3-4-person nominal groups (whose members made independent judgments and later combined the highest and lowest of these estimates into a single confidence interval) were better calibrated than individual judges and interactive groups. This pattern held even when participants were directly instructed to expand their interval estimates, or when interactive groups appointed a devil's advocate or explicitly considered reasons why their interval estimates might be too narrow. Interactive groups did not perform substantially better than individuals, although participants frequently had the impression that group judgments were far superior to individual judgments. This misperception resembles the illusion of group effectivity found in brainstorming research.