Suppose a principal of a large high school wants to survey a sample of five teachers about conditions in the teachers' lounge. For each of the following sampling methods, tell which type of bias causes it to be flawed.
a. The principal randomly selects from a list that does not include the school's parttime teachers.
b. The principal puts a box outside the lounge, indicating that teachers can contribute anonymous comments about the condition of the lounge.
c. The principal thinks of several teachers to ask about conditions in the lounge.
d. A random sample taken from all the school's teachers receive an anonymous survey about the lounge in their mailboxes, with a request for them to complete and return it.
e. Whenever a teacher stops by the principal's office with other concerns, the principal can ask for his or her opinion about the condition of the lounge.