Norman thinks that the brain function of students suffers when they receive less sleep. He predicts that students
who get less sleep before an exam will receive lower test grades. To investigate his idea, he tests two groups of
chemistry students. Group 1 receives four hours of sleep, while Group 2 receives the recommended eight hours
of sleep the night before the exam. Both groups consume the same foods before testing and take the same exam
in the same room. The room has a constant temperature and level of light for all students.
What is the independent variable in Norman's investigation?
• the amount of sleep students receive before their test
•the range of grades students receive on their exam
• the amount of students who receive a failing exam grade
• the brain function of students while taking their exam