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As the automobile accident rate increases, insurers are forced to increase their

ID: 3358742 • Letter: A

Question

As the automobile accident rate increases, insurers are forced to increase their premium rates. Companies such as Allstate have recently been running a campaign they hope will result in fewer accidents by their policyholders. For each six-month period that a customer goes without an accident, Allstate will reduce the customer’s premium rate by a certain percentage. Companies like Allstate have reason to be concerned about driving habits, based on a survey conducted by Volvo of North America, in which 1,100 drivers were surveyed.   Among those surveyed, 74% said that careless or aggressive driving was the biggest threat on the road. One-third of respondents said that cell phone usage by other drivers was the driving behavior that annoyed them the most.

     Based on these data, assuming that the sample was a simple random sample, construct and interpret a 95% confidence interval estimate for the true proportion in the population of all drivers who are annoyed by cell phone users.

Explanation / Answer

given n=1100

p=0.74

95% Confidence interval for P is

where p=0.74 and z=1.96 and n=1100

Hence 95% CI for P is

(0.7141, 0.7659)