For each of the following sampling methods, indicate whether it is random (i.e., whether it gives each member of a specific well-defined population an equal chance of being included) or accidental/convenience sampling. Does it involve stratification; that is, does it involve sampling from members of subgroups, such as males and females or members of various political parties? Is a sample obtained in this manner likely to be representative of some well-defined larger population? Or is it likely to be a biased sample, a sample that does not correspond to any clearly defined population?
a. A teacher administers a survey on math anxiety to the 25 members of her introductory statistics class. The teacher would like to use the results to make inferences about the average levels of math anxiety for all first-year college students in the United States.
b. A student gives out surveys on eating disorder symptoms to members of her teammates in gymnastics. She wants to be able to use her results to describe the correlates of eating disorders in all college women.
c. A researcher sends out 100,000 surveys on problems in personal relationships to mass mailing lists of magazine subscribers. She gets back about 5,000 surveys and writes a book in which she argues that the information provided by respondents is informative about the relationship problems of all American women.
d. The Nielson television ratings organization selects a set of telephone area codes to make sure that its sample will include people taken from every geographical region that has its own area code; it then uses a random number generator to get an additional seven-digit telephone number. It calls every telephone number generated using this combination of methods (all area codes included and random dialing within an area code). If the person who answers the telephone indicates that this is a residence (not a business), that household is recruited into the sample, and the family members are mailed a survey booklet about their television-viewing habits.