Which of the Following Situations Could Cause Bias in the Results

Multiple Choice

Which of the following situations could cause bias in the results of a telephone survey?

A) A phone number in the sample was found to be 'not in service' or 'disconnected'.
B) The person who answered the phone refused to participate.
C) There was no answer, so the interviewer gave up and called someone else.
D) Each of the above would cause bias in the results.