Why Do Studies That Measure Social Cohesion Show a Smaller

Why do studies that measure social cohesion show a smaller cohesion-performance link than those studies that measure task cohesion?

A) Friendship and liking one another are probably not as important to performance as working toward the same goal
B) Social cohesion studies tend to be biased
C) The direction of causality is not established
D) It is much more difficult to get accurate measures of social cohesion than accurate measures of task cohesion