Problem: More on random digit dialing. By the end of 2009, about 25% of adults lived in households with a cell phone and no landline phone, and among adults aged 25 to 29 this number was almost 50%.

Required:

(i) Write a survey question for which the opinions of adults with landline phones only are likely to differ from the opinions of adults with cell phones only. Give the direction of the difference of opinion.

(ii) For the survey question in (a), suppose a survey was conducted using random digit dialing of landline phones only. Would the results be biased? What would be the direction of bias?

(iii) Most surveys now supplement the landline sample contacted by RDD with a second sample of respondents reached through random dialing of cell phone numbers. The landline respondents are weighted to take account of household size and number of telephone lines into the residence, while the cell phone respondents are weighted according to whether they were reachable only by cell phone or also by landline. Explain why it is important to include both a landline sample and a cell phone sample. Why is the number of telephone lines into the residence important? (Hint: How does the number of telephone lines into the residence affect the chance of the household being included in the RDD sample?)