In a Recent Investigation, the National Highway Traffic Safety Administration

question 29

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.

• 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.

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Definitions:

Wilcoxon Signed-Rank Test

A non-parametric statistical test used to compare two related samples, matched samples, or repeated measurements on a single sample to assess whether their population mean ranks differ.

Paired-Difference Experiment

A study design where the subjects are paired up based on certain criteria, and differences within each pair are studied.

Wilcoxon Signed-Rank Test

A non-parametric test used to compare two related samples, matched samples, or repeated measurements on a single sample to assess whether their population mean ranks differ.

Large-Sample Z-Test

A statistical hypothesis test used when the sample size is large, generally over 30, utilizing the standard normal distribution.