Respuesta :
Answer:
The point estimate that should be used in constructing the confidence interval is 3.5.
The 95% confidence interval for the true mean difference between the mean height of the American students and the mean height of the non-American students, in inches, is (2.25, 4.75).
Step-by-step explanation:
Before building the confidence interval, we need to understand the central limit theorem and subtraction of normal variables.
Central Limit Theorem
The Central Limit Theorem establishes that, for a normally distributed random variable X, with mean [tex]\mu[/tex] and standard deviation [tex]\sigma[/tex], the sampling distribution of the sample means with size n can be approximated to a normal distribution with mean [tex]\mu[/tex] and standard deviation [tex]s = \frac{\sigma}{\sqrt{n}}[/tex].
For a skewed variable, the Central Limit Theorem can also be applied, as long as n is at least 30.
Subtraction between normal variables:
When two normal variables are subtracted, the mean is the difference of the means, while the standard deviation is the square root of the sum of the variances.
American students:
Sample of 12, mean height of 68.4 inches with a standard deviation of 1.64 inches. This means that:
[tex]\mu_A = 68.4[/tex]
[tex]s_A = \frac{1.64}{\sqrt{12}} = 0.4743[/tex]
Non-American students:
Sample of 17, mean height of 64.9 inches with a standard deviation of 1.75 inches. This means that:
[tex]\mu_N = 64.9[/tex]
[tex]s_N = \frac{1.75}{\sqrt{17}} = 0.4244[/tex]
Distribution of the difference:
[tex]\mu = \mu_A - \mu_N = 68.4 - 64.9 = 3.5[/tex]
[tex]s = \sqrt{s_A^2+s_N^2} = \sqrt{0.4743^2 + 0.4244^2} = 0.6365[/tex]
The point estimate that should be used in constructing the confidence interval is 3.5.
Confidence interval:
[tex]\mu \pm zs[/tex]
In which
z is the z-score that has a p-value of [tex]1 - \frac{\alpha}{2}[/tex].
95% confidence level
So [tex]\alpha = 0.05[/tex], z is the value of Z that has a p-value of [tex]1 - \frac{0.05}{2} = 0.975[/tex], so [tex]Z = 1.96[/tex].
The lower bound of the interval is:
[tex]\mu - zs = 3.5 - 1.96*0.6365 = 2.25[/tex]
The upper bound of the interval is:
[tex]\mu + zs = 3.5 + 1.96*0.6365 = 4.75[/tex]
The 95% confidence interval for the true mean difference between the mean height of the American students and the mean height of the non-American students, in inches, is (2.25, 4.75).
