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 52 records of automobile driver fatalities in a certain county showed that 32 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 α = 0.05.

(a) What is the level of significance? State the null and alternate hypotheses.

H0: p = 0.77; H1: p > 0.77

H0: p = 0.77; H1: p < 0.77

H0: p < 0.77; H1: p = 0.77

H0: p = 0.77; H1: p ≠ 0.77

(b) What sampling distribution will you use?

The standard normal, since np < 5 and nq < 5.

The Student's t, since np < 5 and nq < 5.

The Student's t, since np > 5 and nq > 5.

The standard normal, since np > 5 and nq > 5.

What is the value of the sample test statistic? (Round your answer to two decimal places.)

(c) Find the P-value of the test statistic. (Round your answer to four decimal places.)

Sketch the sampling distribution and show the area corresponding to the P-value.

(d) Based on your answers in parts (a) to (c), will you reject or fail to reject the null hypothesis? Are the data statistically significant at level α?

At the α = 0.05 level, we reject the null hypothesis and conclude the data are statistically significant.

At the α = 0.05 level, we reject the null hypothesis and conclude the data are not statistically significant.

At the α = 0.05 level, we fail to reject the null hypothesis and conclude the data are statistically significant.

At the α = 0.05 level, we fail to reject the null hypothesis and conclude the data are not statistically significant.

(e) Interpret your conclusion in the context of the application.

There is sufficient evidence at the 0.05 level to conclude that the true proportion of driver fatalities related to alcohol in the county is less than 0.77.

There is insufficient evidence at the 0.05 level to conclude that the true proportion of driver fatalities related to alcohol in the county is less than 0.77.

Answer 1

a) H₀: P = 0.77

   H₁: P < 0.77

b) The standard normal, since np > 5 and nq > 5 .

= 32/52 = 0.615

The test statistic z = ( - P)/sqrt(P(1 - P)/n)

                            = (0.615 - 0.77)/sqrt(0.77 * (1 - 0.77)/52)

                            = -2.66

c) P-value = P(Z < -2.66)

               = 0.0039

d) Since the P-value is less than (0.0039 < 0.05), we should reject the null hypothesis.

At the = 0.05 level, we reject the null hypothesis and conclude the data are statistically significant.

e) There is sufficient evidence at the 0.05 level to conclude that the true proportion of driver fatalities related to alcohol in the country is less than 0.77