Question

In a survey of 140 undergraduate students in an elementary statistics class at UW, 12 said they were left-handed and 128 said they were right-handed. Assume the students are representative of all UW undergrads. Do these data provide evidence that the proportion of UW undergrads who are left-handed differs from the national proportion of 0.10 at the 5% significance level?

data: 12 out of 140, null probability 0.1 z = 0.563, p-value = 0.5731 alternative hypothesis: true p is not equal to 0.1 95 percent confidence interval: 0.04971124 0.14384532 sample estimates: P 0.08571429
a) Define the null and alternative hypothesis for answering the question being asked. Define both in words and in symbols.
b) The R output for running this test is shown below. What do you conclude for this test? Include your decision and an interpretation in the context of the problem. Be specific.
c) Explain in words what the p-value of 0.5731 means.

Answer 1

a) The null hypothesis, H₀; p = 0.1

The alternative hypothesis, Hₐ; p ≠ 0.1

b) The proportion of left handed undergrads in UW differs from the national proportion of 0.1

c) The p-value is larger than the level of significance therefore there is statistical evidence supporting the alternative hypothesis

Explanation:

The given data are;

The number of students in the sample, n = 140

The number of left handed students in the sample = 12

The number of right handed students in the sample = 128

The proportion of left handed students in the sample,
`\hat p` = 12/140 = 0.08571429

The significance level = 5%

The national proportion, p₀ = 0.1

a) The null hypothesis, H₀; p = 0.1

The null hypothesis is the proportion of left handed students in the UW is the same as the national proportion of 0.1

The alternative hypothesis, Hₐ; p ≠ 0.1

The alternative hypothesis is the proportion of left handed students in the UW is not the same as the national proportion of 0.1

b) Given from the output values of the Confidence Interval at 95% confidence level, (0.04971124, 0.14384532) which are both positive values, and the p-value of 0.5731, we conclude that there is a difference between the proportion of left-handed UW undergraduate students and the national proportion of 0.1

c) Given that the p-value of 0.5731 is larger than the significance level of 0.05, we reject the null hypothesis and there is significant statistical evidence to suggest that the proportion of UW undergrads who are left handed differs from the national proportion of 0.10