Since Ringelmann in 1913 we’ve known that individual performance tends to decrease with increasing group size. (Ringelmann’s original study involved a tug-of-war between two teams). Ringelmann attributed the effect mainly to the increasingly challenging coordination in larger groups (see the beta coherence term in the USL). There are also social factors at work: the tendency of group members to spend less effort in larger groups is generally attributed to situations characterized by a lack of individual accountability and shared responsibility.
"Люблю групповуху. Можно сачкануть". ‎- сексизм и радиофобия