The website www.ratemyprofessors .com provides students an opportunity to view ratings for instructors at their universities. A group of students planning to register for a statistics course in the upcoming semester are trying to identify the instructors who receive the highest ratings on the site. One student decides to register for Professor Smith’s course because she has the best ratings of all statistics instructors. Another student
comments:

a. The website ratings are unreliable because the ratings are from students who voluntarily visit the site to rate their instructors.
b. To obtain reliable information about Professor Smith, they would need to take a simple random sample of the 78 ratings left by students on the site and compile new overall ratings based on those in the random sample. Which, if either, of the student’s comments are valid?