An airport administrator investigated the attention spans of air traffic controllers to determine how many incoming flights the average controller can coordinate at the same time. Each randomly selected controller was tested, without his or her knowledge, by a computer program that fed false flight information to a computer terminal. The controller first "received" information from one plane, and by the end of an hour the controller was coordinating 10 planes simultaneously. The administrator analyzed the errors collected by the computer program. The analysis revealed that the maximum number of planes a controller could handle without making potentially fatal errors was six planes. Also, no errors occurred when only one to three planes were incoming. He concluded that a controller should never coordinate more than six incoming flights.

Are the researcher's conclusions warranted?
Name the independent variable(s):
Name the dependent variable(s):
Name the confounded variable(s):