A cognitive psychologist's theory predicts that sleep deprivation impairs memory. She randomly assigns 20 college students into three groups, Groups A, B and C. All of the students read the same short story. Later, over an 8-hour period, Group A is allowed to sleep undisturbed, Group B is allowed 4 hours sleep and Group C is allowed 2 hours sleep. All students are then asked to answer questions about the story they read. The psychologist then compares memory performance among the three groups, draws conclusions and publishes her findings. The following terms apply to various components of the experiment