Sequential human redundancy: Can social loafing diminish the safety of double checks?

It is often assumed that if two people work on a failure-detection task one after the other, they will observe more failures than when only one person undertakes the task (4-eyes principle). However, human beings have also been found to exert less effort on tasks that they share responsibility for, a phenomenon called . In the current research, we assessed the effectiveness of sequential human redundancy in light of possible social loafing. In two laboratory experiments, teams of two participants performed a quality-control task in a blinded and in a nonblinded condition, operationally defined by whether or not evaluations of the first checker were forwarded to the second one. In the blinded condition, no social loafing was found, and a near-perfect overall team performance was observed. In contrast, nonblinded redundancy led to a substantial effort reduction of the second checker. However, despite this social-loafing effect at the second position, even nonblinded redundancy led to an overall safety advantage over a single-checker condition. Our research suggests that social loafing in sequential-human-redundancy work settings can occur but does not necessarily reduce the gains in overall reliability. Blinded processes, however, seem to provoke less social loafing than nonblinded processes. (PsycInfo Database Record (c) 2023 APA, all rights reserved).