A local cable TV com-pany, Pacific TV (PTV), with customers in 15 towns is considering offering high-speed Internet service on its cable lines. Before launching the new service they want to find out whether customers would pay the $7 5 per month that they plan to charge. An intern has prepared several alternative plans for assessing customer demand. For each, indicate what kind of sampling strategy is involved and what (if any) biases might result.
a) Put a big ad in the newspaper asking people to log their opinions on the PTV website.
b) Randomly select one of the towns and contact every cable subscriber by phone.
c) Send a survey to each customer and ask them to fill it out and return it.
d) Randomly select 20 customers from each town. Send them a survey, and follow up with a phone call if they do not return the survey within a week.