Wilson v USA and Boy Scouts of America, 989 F2d 953 (8th Cir 1993) gives the universal rule of law.  “Under the doctrine of respondeat superior an employer is liable for the negligent acts or omissions of his employee which are committed within the scope of his employment. Liability based on respondeat superior requires some evidence that a master-servant relationship existed between the parties. The test to determine if respondeat superior applies is whether the person sought to be charged as a master had “the right or power to control and direct the physical conduct of the other in the performance of the act.” If there is no right to control, there is no liability.

This case arose out of a Boy Scout camping trip at a military post.   Three boys got into some activities outside while their leaders were inside and were electrocuted.   In finding that neither of the defendants had vicarious liability the court used clarifying language such as no consent to control,  no supervisory powers over the method or manner of accomplishing tasks,  and no direct control over the specific activities at the lowest level.