Question

The U.S. Department of Transportation, National Highway Traffic Safety Administration, reported that 77% of all fatally injured automobile drivers were intoxicated. A random sample of 25 records of automobile driver fatalities in Kit Carson County, Colorado, showed that 14 involved an intoxicated driver. Do these data indicate that the population proportion of driver fatalities related to alcohol is less than 77% in Kit Carson County? Use ? = 0.01. Solve the problem using both the traditional method and the P-value method. Since the sampling distribution of p? is the normal distribution, you can use critical values from the standard normal distribution as shown in the table of critical values of the zdistribution. (Round the test statistic and the critical value to two decimal places. Round the P-value to four decimal places.)

test statistic	=
critical value	=
P-value	=

State your conclusion in the context of the application.

(a)There is sufficient evidence at the 0.01 level to conclude that the true proportion of driver fatalities related to alcohol is less than 77%.

(b)There is insufficient evidence at the 0.01 level to conclude that the true proportion of driver fatalities related to alcohol is less than 77%.    

Compare your conclusion with the conclusion obtained by using the P-value method. Are they the same?

(a) The conclusions obtained by using both methods are the same.

(b) We reject the null hypothesis using the P-value method, but fail to reject using the traditional method.

(c) We reject the null hypothesis using the traditional method, but fail to reject using the P-value method.

Answer 1

Solution: Test statistic is given below:

Where is the sample proportion

  

Therefore the test statistic is

Left tailed Critical value at 0.01 significance level is

Therefore the critical value is

P- value is given below:

Using the standard Normal table we have:

State your conclusion in the context of the application.

Answer: (a)There is sufficient evidence at the 0.01 level to conclude that the true proportion of driver fatalities related to alcohol is less than 77%.

Compare your conclusion with the conclusion obtained by using the P-value method. Are they the same?

Answer: (a) The conclusions obtained by using both methods are the same.