Gulf oil spill

Problem: Two months after the Gulf oil spill began in April 2010, nearly half of Americans (49%) believed that at least some of the affected beaches will never recover, according to a Gallup Poll conducted June 11 to 13, 2010. Results are based on telephone interviews of a random sample of 1014 adults, aged 18 and older, selected using random digit dialing sampling. In the survey methods section, Gallup reports: "Interviews are conducted with respondents on landline tele phones (for respondents with a landline telephone) and cellular phones (for respondents who are cell phone-only). Each sample includes a minimum quota of 150 cell phone-only respondents and 850 landline respondents, with additional minimum quotas among landline respondents for gender within region."23

Required:

(a) What is automated random digit dialing? Why is it a practical method for obtaining (almost) an SRS of households with landline phones?

(b) The survey wants the opinion of an individual adult. Several adults may live in a household. In that case, the survey interviewed the adult with the most recent birthday. Why is this preferable to simply interviewing the person who answers the phone?

(c) The survey included both landline telephones and cellular phones. Why do you think this may be important? Sampling landline telephones and cellular phones separately corresponds to what type of sampling design?