Chi-Square Hypothesis Test
Each year, the National Highway Traffic Safety Administration
(NHTSA) together with the National Center for Statistics and
Analysis (NCSA) publishes Traffic Safety Facts, which summarizes
the motor vehicle traffic crash experience for the United States.
Traffic Safety Facts 2001 includes trend data, crash data, vehicle data,
and people data. Also, the NHTSA and NCSA publish a report
summarizing the motor vehicle crash data of the 17 states in the
NHTSA’s State Data System.
In 2001, there were 42,116 fatalities in the United States as a
result of motor vehicle crashes. The pie chart at the right shows the
national distribution of traffic fatalities with respect to age group. For
example, 24% of all motor vehicle fatalities were young adults aged
16-24. Using the data from the 17 states in the NHTSA’s State Data
System as a sample, the contingency table shows the number of motor
vehicle fatalities according to age and geographic location within the
1. In 2001, how many people in the United States aged 16-24 died as a result of a motor vehicle crash?
2. Assuming the variables region and age are independent, in which region did the number of motor vehicle fatalities for the 16-24 age group exceed the expected number of fatalities?
3. Assuming the variables region and age are independent, in which region did the number of motor vehicle fatalities for the 25-34 age group exceed the expected number of fatalities?
4. At a = 0.05, perform a chi-square test to determine whether the variables region and age are independent. What can you conclude?