Question 3.27

3.27 What’s wrong?

Explain what is wrong with each of the following random selection procedures, and explain how you would do the randomization correctly.

  1. To determine the reading level of an introductory statistics text, you evaluate all of the written material in the third chapter.
  2. You want to sample student opinions about a proposed change in procedures for changing majors. You hand out questionnaires to 100 students as they arrive for class at 7:30 A.M.
  3. A population of subjects is put in alphabetical order, and a simple random sample of size 10 is taken by selecting the first 10 subjects in the list.

3.27

(a) Material from the third chapter is likely not representative of the reading level for the entire book. One example of how to randomize is to randomly select pages and evaluate the reading level of these. (b) Students who attend a particular class at 7:30 a.m. are certainly not representative of all students. A list of all students needs to be used in which you randomly selected 100 to participate. (c) Taking subjects from the top or bottom of an alphabetized list gives different chances of being selected that taking subjects based on the first letter of their name and is not equally likely. Using number assignments and random digits is an appropriate selection process.