Publishers of a magazine wish to determine what proportion of the magazine's 50,000 subscribers are pleased with their subscription. The publishers intend to mail a survey to 1,000 subscribers randomly selected from those who have received the magazine for 5 years or more. This introduces selection bias, since long-subscribing customers are more likely to be pleased with their subscription. Which of the following would best eliminate selection bias? a. Mail surveys to 2,000 subscribers randomly selected from those who have received the magazine for 5 years or more.
b. Mail surveys to 1,000 subscribers randomly selected from those who have received the magazine for 1 year or less.
c. Mail surveys to 1,000 subscribers randomly selected from all subscribers.
d. Mail surveys to 1,000 subscribers randomly selected from those who have received the magazine for 5 years or more and 1,000 subscribers randomly selected from those who have received the magazine for 1 year or less.
e. Mail surveys to 500 subscribers randomly selected from a group who have received a free six-month subscription within the past year.