Interviews
Each interview will be 10 minutes, conducted over Zoom and recorded.
You will sign up for an interview slot with an instructor before each
interview.
Interview 1
Overview
In Interview 1, you will be presented with a question and some data. First, we will read the question to you.
It is a good idea to have a pencil and paper handy and take notes.
After you have had a chance to think about the question and ask any clarifying questions, you will
share your full screen. You may be asked to do the following:
- state the null and alternative hypothesis
- explain what a Type I or Type II error is in the context of the question
- show how to simulate the P-value using the box model applet
- show how to simulate the P-value using R
- show how to test the null hypothesis using the binomial or hypergeometric model, using R to do the calculations
- state your conclusion in the context of the question
You should have both the box model applet and R open on your computer
when you share your screen. You may have a sheet of notes to refer to during your interview.
Every student in the class will get a unique question, but all questions will be similar to the sample questions below.
Sample Questions
- Advances in medical care such as prenatal ultrasound examination now make it possible to determine a child's sex early in a pregnancy. There is a fear that some parents may use this technology to select the sex of their children. At a hospital one month, 38 out of 60 live births were boys. Does this suggest that parents in that region are selecting male babies? (Note: There is a 51% chance that a given baby will be male.)
- In 1969, Dr. Spock came to trial before Judge Ford, in Boston's federal court house. The jury was drawn from a "venire," or panel, of 350 persons selected by the clerk, of which 102 were women. At the next stage in selecting the jury to hear the case, Judge Ford chose 100 potential jurors out of these 350 persons. His choices included 9 women. Does Judge Ford seem to be discriminating against women?
- According to the National Institute of Occupational Safety and Health, job stress poses a major threat to the health of
workers. A national survey of restaurant employees found that 75% said that work stress had a negative impact on their personal
lives. A sample of 100 employees of a restaurant chain finds that 68 answer "Yes" when asked, "Does work stress have a negative
impact on your personal life?" Is this good reason to think that the proportion of all employees of this chain who would say
"Yes" differs from the national percentage of 75%?
- A study of the effects of acid rains on trees in the Hopkins Forest shows that 25 of 100 trees sampled exhibit some sort of
damage from acid rain. This rate seemed to be higher than the 15% quoted in a recent Environmetrics article on the
average proportion of damaged trees in the Northeast. Does the sample suggest that trees in the Hopkins Forest are more
susceptible than trees from the rest of the region?
Rubric
- state hypotheses: 4 points
- explain Type I or Type II error: 4 points
- set up box model: 4 points
- calculate P-value using simulation: 4 points
- calculate exact P-value: 4 points
- state conclusion: 4 points
Total: 24 points
Please see Canvas for a more detailed description of each rubric item.
Logistics
All interviews will be held on Monday, October 16. Click here to sign up for the interview.
Interview 2
Overview
In Interview 2, you will be presented with a question and some data. First, we will read the question to you.
It is a good idea to have a pencil and paper handy and take notes.
After you have had a chance to think about the question and ask any clarifying questions, you will
share your full screen. You may be asked to do the following:
- identify the parameter of interest (\(p\) or \(\mu\))
- describe the box model to the best of your ability (you don't need to set it up in the applet)
- state the assumptions necessary for the confidence interval to be valid
- construct and interpret a confidence interval for the parameter
- based on the interval, state the conclusion of a hypothesis test for a specific value of the parameter
- determine the sample size needed to achieve a certain margin of error
You should have R open on your computer when you share your screen.
You may have a sheet of notes to refer to during your interview.
Every student in the class will get a unique question, but all questions will be similar to the sample questions below.
Sample Questions
-
Kellogg's controls a 43% share of the cereal market worldwide.
Their signature cereal is Corn Flakes. Suppose the weights of full boxes of Corn Flakes have a standard deviation of
0.29 ounces. A random sample of 25 boxes produced a mean weight of 9.82 ounces.
- Define an appropriate parameter and construct an 80% confidence interval for that parameter.
- The Corn Flakes box advertises a weight of 9.90 ounces. Based on your interval, what would
happen if we were to test that null hypothesis?
- What sample size would be needed if we wanted to estimate the average weight to within \(\pm 0.05\) grams with 80% confidence?
-
In November 2011, Pew Research polled a random sample of 799 U.S. teens about Internet use. 392 of those
teens reported that they had misrepresented their age online to gain access to websites and online services.
- Define an appropriate parameter and construct a 99% confidence interval for that parameter.
- Based on the interval, what would happen if we were to test the null hypothesis that 50% of U.S. teens misrepresent their age online?
- What sample size would be needed if we wanted the 99% confidence interval to be no more than 1% wide?
-
Students investigating the packaging of potato chips purchased 6 bags of Lay's Ruffles marked with a
net weight of 28.3 grams. They carefully weighed the contents of each bag, recording the following weights
(in grams): 29.3, 28.2, 29.1, 28.7, 28.9, 28.5.
- Define an appropriate parameter and construct a 95% confidence interval for that parameter.
- Based on the interval, what would happen if we were to test the null hypothesis that the average net weight is 28.3 grams?
- What sample size would be needed if we wanted to estimate the average net weight to within \(\pm 0.1\) grams with 95% confidence?
Rubric
- state the parameter: 4 points
- describe the box model and state assumptions: 4 points
- construct the confidence interval: 4 points
- interpret the confidence interval: 4 points
- state the conclusion of a hypothesis test: 4 points
- calculate the sample size for a given margin of error: 4 points
Total: 24 points
Please see Canvas for a more detailed description of each rubric item.
Logistics
All interviews will be held on Monday, November 13. Click here to sign up for the interview.