Question

A professor is interested in how the 500 students in his class will rate today's lecture. He selects the first 30 students on his class list, reads the names at the beginning of the lecture, and asks them to go online to the course Web site and rate the lecture on a scale of 0 to 5. Which of the following is the most important reason why a confidence interval for the mean rating by all his students based on these data is of little use?

Answer 1

the rating by taking the first 30 students on his class list isn't random. to get a good confidencen interval, the sample of students should be random, not a list.