motivation

You exert less individual effort when working in groups.

The phenomenon of reduced individual output in groups is known as the Ringelmann effect, which was later named social loafing in 1979.

Ringelmann conducted his research in the 1880s; the term 'social loafing' was coined by Latané, Williams, and Harkins in 1979.

The collective output often masks individual decline.

Where this comes from

Study: Max Ringelmann, 1913, though replicated extensively in later group dynamics research
What the check found: The phenomenon was discovered by Ringelmann in the 1880s, but the term and theoretical framework of social loafing were established much later in 1979.
Confidence: Solid, with limits

One of these every day, and every one names the study it came from. When a finding is contested, it says so.