The National Highway Traffic Safety Administration (NHTSA) conducted a survey to learn about how drivers throughout the United States are using seat belts (Associated Press, August 25, 2003). Sample data consistent with the NHTSA survey are as follows. Driver Using Seat Belt? Region Yes No Northeast 148 52 Midwest 162 54 South 296 74 West 252 48 Total 858 228
a. For the United States, what is the probability that a driver is using a seat belt?
b. The seat belt usage probability for a U.S. driver a year earlier was .75. NHTSA chief Dr. Jeffrey Runge had hoped for a .78 probability in 2003. Would he have been pleased with the 2003 survey results?
c. What is the probability of seat belt usage by region of the country? What region has the highest seat belt usage?
d. What proportion of the drivers in the sample came from each region of the country? What region had the most drivers selected? What region had the second most drivers selected?
e. Assuming the total number of drivers in each region is the same, do you see any reason why the probability estimate in part (a) might be too high? Explain.