Small groups outperform large groups and individuals in tasks with asymmetric accuracy

Aggregating decisions from larger groups often improves accuracy compared to individuals or smaller groups. Most studies assume that accuracy is the same when the event occurs and when it does not, yet individuals can be more competent in detecting when it occurs than when it does not, or vice versa. This study emphasizes the importance of individual competencies in the form of hits (h, e.g., a jury member correctly votes guilty) and correct rejections (cr, e.g., a jury member correctly votes not guilty). Small groups outperform individuals and larger groups in a single task when the average individual proportion correct exceeds .5, h and cr are asymmetric around .5, and h+cr>1. When the average proportion correct is below .5 and h+cr<1, small groups perform worse than individuals and larger groups. These findings are supported by empirical data on violent recidivism, psychiatric morbidity, anxiety, and deception detection, and also highlight how decision correlations can both aid and hinder small group performance.