Does sleep deprivation affect academic performance? Researchers surveyed a sample of 820 college students. Among the questions asked was whether or not the student had experienced at least one night of total sleep deprivation (known as pulling an "all- nighter") since beginning college. Researchers were also able to obtain grade point average (or GPA) information about each student from the college registrar. It was observed that students who pulled more "all-nighters" had lower GPAs than students who pulled fewer "all-nighters." We would not want to conclude that pulling an "all-nighter" causes a college student to have a lower GPA because A. we don't know if the sample was randomly selected from the population. B. an experiment was not conducted. C. the sample size is too small. D. Both A and B are correct answers. E. A. B, and C are all correct answers.