Answer:
The 90% confidence interval for the difference between the proportions of male and female students who were employed during the summer is (0.01, 0.1012).
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
and standard deviation
, the sampling distribution of the sample means with size n can be approximated to a normal distribution with mean
and standard deviation
.
For a skewed variable, the Central Limit Theorem can also be applied, as long as n is at least 30.
For a proportion p in a sample of size n, the sampling distribution of the sample proportion will be approximately normal with mean
and standard deviation
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.
Male undergraduates:
670, 388 were employed. So
![p_M = \frac{388}{670} = 0.5791](https://tex.z-dn.net/?f=p_M%20%3D%20%5Cfrac%7B388%7D%7B670%7D%20%3D%200.5791)
![s_M = \sqrt{\frac{0.5791*0.4209}{670}} = 0.0191](https://tex.z-dn.net/?f=s_M%20%3D%20%5Csqrt%7B%5Cfrac%7B0.5791%2A0.4209%7D%7B670%7D%7D%20%3D%200.0191)
Female undergraduates:
Of 617, 323 were employed. So
![p_F = \frac{323}{617} = 0.5235](https://tex.z-dn.net/?f=p_F%20%3D%20%5Cfrac%7B323%7D%7B617%7D%20%3D%200.5235)
![s_F = \sqrt{\frac{0.5235*0.4765}{617}} = 0.0201](https://tex.z-dn.net/?f=s_F%20%3D%20%5Csqrt%7B%5Cfrac%7B0.5235%2A0.4765%7D%7B617%7D%7D%20%3D%200.0201)
Distribution of the difference:
![p = p_M - p_F = 0.5791 - 0.5235 = 0.0556](https://tex.z-dn.net/?f=p%20%3D%20p_M%20-%20p_F%20%3D%200.5791%20-%200.5235%20%3D%200.0556)
![s = sqrt{s_M^2+s_F^2} = \sqrt{0.0201^2 + 0.0191^2} = 0.0277](https://tex.z-dn.net/?f=s%20%3D%20sqrt%7Bs_M%5E2%2Bs_F%5E2%7D%20%3D%20%5Csqrt%7B0.0201%5E2%20%2B%200.0191%5E2%7D%20%3D%200.0277)
Confidence interval:
The confidence interval is given by:
![p \pm zs](https://tex.z-dn.net/?f=p%20%5Cpm%20zs)
In which
z is the z-score that has a p-value of
.
90% confidence level
So
, z is the value of Z that has a p-value of
, so
.
The lower bound of the interval is:
![p - zs = 0.0556 - 1.645*0.0277 = 0.01](https://tex.z-dn.net/?f=p%20-%20zs%20%3D%200.0556%20-%201.645%2A0.0277%20%3D%200.01)
The upper bound of the interval is:
![p + zs = 0.0556 + 1.645*0.0277 = 0.1012](https://tex.z-dn.net/?f=p%20%2B%20zs%20%3D%200.0556%20%2B%201.645%2A0.0277%20%3D%200.1012)
The 90% confidence interval for the difference between the proportions of male and female students who were employed during the summer is (0.01, 0.1012).