In a Recent Investigation, the National Highway Traffic Safety Administration

Essay

In a recent investigation, the National Highway Traffic Safety Administration (NHTSA) found that the Chevrolet Volt and other electric vehicles do not pose a greater risk of fire than gasoline-powered vehicles (The Boston Globe, January 25, 2012). Specifically, it was determined that "no discernible defect trend exists." Suppose a consumer advocacy group wants to verify some of these claims by constructing a chart. The group expects 2% of electric cars to catch fire each month. For each of the last six months, 500 electric car owners are asked if their cars have caught fire. These sample proportions are obtained:
0.010 0.020 0.015 0.030 0.025 0.015.
A) Assuming that the group expectation is correct, construct the centerline and the upper and lower control limits for the chart.
B) Do the consumer group's findings support those of the NHTSA? Explain the answer.