Final answer:
The decline in individual productivity within larger groups due to less identifiable contributions is known as social loafing.
Step-by-step explanation:
The phenomenon referred to in the research on group productivity in the United States, where individual productivity tends to decline in larger groups, is known as social loafing. This effect occurs when individuals exert less effort in a group setting because their personal contributions are less identifiable, leading to reduced performance on relatively easy tasks. Research has demonstrated that social loafing is more prevalent in certain demographics, such as college students, and less so among women and those from collectivistic cultures. When the tasks are complex and challenging, however, the opposite effect can occur, with individuals feeling motivated to contribute significantly to their group's efforts.
There are distinct differences between small and large groups in terms of accountability and cohesion. In small groups, individual efforts are more visible and hence more likely to be noticed if someone decides to free ride.