In: Statistics and Probability
4. The highway department is testing two types of reflecting
paint for concrete bridge end pillars. The two kinds of paint are
alike in every respect except that one is orange and the other is
yellow. The orange paint is applied to 12 bridges, and the yellow
paint is applied to 12 bridges. After a period of 1 year,
reflectometer readings were made on all these bridge end pillars.
(A higher reading means better visibility.) For the orange paint,
the mean reflectometer reading was x1 = 9.4,
with standard deviation s1 = 2.1. For the
yellow paint the mean was x2 = 6.9, with
standard deviation s2 = 2.5. Based on the data,
can we conclude that the yellow paint has less visibility after 1
year? Use a 1% level of significance.
a. What are we testing in this problem?
1. difference of proportions
2. difference of means
3. single mean
4. paired difference
5. single proportion
b. What is the level of significance?
c. State the null and alternate hypotheses.
H0: μ1 ≥ μ2; H1: μ1 < μ2
H0: μ1 ≤ μ2; H1: μ1 > μ2
H0: μ1 = μ2; H1: μ1 ≠ μ2
H0: μ1 ≠ μ2; H1: μ1 = μ2
d. What sampling distribution will you use? What
assumptions are you making?
The Student's t. We assume that both population distributions are approximately normal with known population standard deviations.
The Student's t. We assume that both population distributions are approximately normal with unknown population standard deviations.
The standard normal. We assume that both population distributions are approximately normal with unknown population standard deviations.
The standard normal. We assume that both population distributions are approximately normal with known population standard deviations.
e. What is the value of the sample test statistic? (Test
the difference μ1 − μ2.
Round your answer to three decimal places.)
f. Estimate the P-value.
P-value > 0.250
0.125 < P-value < 0.250
0.050 < P-value < 0.1250.025 < P-value < 0.050
0.005 < P-value < 0.025
P-value < 0.005
g. Sketch the sampling distribution and show the area
corresponding to the P-value.
h. Will you reject or fail to reject the null hypothesis?
Are the data statistically significant at level
α?
At the α = 0.01 level, we reject the null hypothesis and conclude the data are statistically significant.
At the α = 0.01 level, we fail to reject the null hypothesis and conclude the data are not statistically significant.
At the α = 0.01 level, we reject the null hypothesis and conclude the data are not statistically significant.
At the α = 0.01 level, we fail to reject the null hypothesis and conclude the data are statistically significant.
i. Interpret your conclusion in the context of the
application.
There is sufficient evidence at the 0.01 level that the yellow paint has less visibility after 1 year.
There is insufficient evidence at the 0.01 level that the yellow paint has less visibility after 1 year.