A voter receives a call in which the caller claims to be conducting a national opinion research poll. The voter is asked if his or her opinion about a congressional candidate would change if he or she knew that the candidate once had a car crash while driving under the influence of alcohol. Identify and explain at least one source of bias in the study described. Then suggest how the bias might have been avoided?

a. The data do not seem to support the claims being made by the study. The researcher should consult an expert to make sure that he or she is correctly interpreting the data.
b. The study does not appear to have a​ well-defined goal. The researcher should determine his or her goal and precisely define the variables of interest.
c. Since the sample is​ self-selected, there is a definite participation bias in this study. The researcher should randomly select the subjects of the study.
d. The wording of the question is biased to strengthen opposition against a particular candidate. The question wording should be changed to be more neutral.