Radio and television stations often air controversial issues during broadcast time and ask viewers to indicate their agreement or disagreement with a given stand on the issue. A poll is conducted by asking those viewers who agree to call a certain 900 telephone number and those who disagree to call a second 900 telephone number. All respondents pay a fee for their calls.
a. Does this polling technique result in a random sample?
b. What can be said about the validity of the results of such a survey? Do you need to worry about a margin of error in this case?