Aresearcher wanted to test the effect of caffeine on sleep. fifty students volunteered to participate in the study and signed up for one of two nights. thirty-three students participated on tuesday night. they each were given two cups of regular coffee to drink one hour before going to sleep. seventeen students participated on wednesday night. they each were given two cups of decaffeinated coffee to drink one hour before going to sleep. each student was monitored with an eeg (a test that looks at brain function) to record exactly when they fell asleep. students in the caffeine group took significantly longer to fall asleep. the researcher concluded that caffeine interferes with the ability to fall asleep. in the experiment, the control group is/are the