Interviews
Each interview will be 10 minutes, conducted in person, during your scheduled tutorial time.
You will need to bring your laptop.
When you arrive at the interview, you will log onto a Zoom call
which will record the interview. You will share your full screen
during the interview.
No notes or other devices are allowed during the interview. However, you may bring a
blank sheet of scratch paper and a pen.
Interview 1
Overview
In Interview 1, you will be presented with a question and some data. First, we will read the question to you.
After you have had a chance to think about the question and ask any clarifying questions, 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 or R
- show how to calculate the exact P-value using the binomial or hypergeometric distribution (in R)
- 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.
Every student in the class will get a unique question, but they 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?
Answers
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
To be held during tutorial times, October 16-17.
Interview 2
Overview
In Interview 2, you will be presented with a question and some data from a randomized experiment.
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:
- describe the experimental design
- state the null and alternative hypotheses
- test the null hypothesis in the potential outcomes applet
- test the null hypothesis or form a confidence interval using the normal approximation in R
- state your conclusion in the context of the question
You should have both the potential outcomes applet and R/RStudio open on your computer when you share your screen.
Every student in the class will get a unique question, but all questions will be similar to the sample questions below.
Sample Questions
- A plant physiologist investigated the effect of mechanical stress
on the growth of soybean plants. Individually potted seedlings were
divided into two groups. Those in the first group were stressed by
shaking for 20 minutes twice daily, while those in the second group
were not shaken. After 16 days of growth the plants were harvested
and total leaf area (in square cm) was measured for each plant.
| Control |
Stressed |
| 314 | 283 |
| 320 | 312 |
| 310 | 291 |
| 340 | 259 |
| 299 | 216 |
| 268 | 201 |
Does this provide convincing evidence that stressing soybean plants
affects their growth?
- 14 volunteer males with high blood pressure were assigned
to one of two diets for four weeks: a fish oil diet and a
standard oil diet. The reductions in diastolic blood pressure (in mm of mercury)
are shown below.
| Fish oil diet: |
8 |
12 |
10 |
14 |
2 |
0 |
0 |
| Regular oil diet: |
-6 |
0 |
1 |
2 |
-3 |
-4 |
2 |
Does this provide evidence that fish oil reduces high blood pressure?
-
Some soap manufacturers sell special "antibacterial" soaps.
However, one might expect ordinary soap to also kill bacteria. To
investigate this, a researcher prepared a solution from ordinary,
nonantibiotic soap and another solution of sterile water. The
two solutions were placed onto petri dishes and E. coli
bacteria were added. The dishes were incubated for 24 hours
and the number of bacteria colonies on each dish were counted.
These numbers are recorded below.
| Soap: |
76 |
27 |
16 |
30 |
26 |
46 |
6 |
| Water: |
30 |
36 |
66 |
21 |
63 |
38 |
35 |
45 |
Does this data provide convincing evidence that ordinary,
nonantibiotic soap kills bacteria?
-
The Spacelab Life Sciences mission was a series of flights that
studied life sciences in space. As part of this study, 14 male rats
were sent to space. Upon their return, the red blood cell mass
(in milliliters) of the rats was determined. A control group of
14 male rats stayed on Earth, and their red blood cell mass was
also determined when the space rats returned. The data is
recorded below.
| Flight |
Control |
| 8.59 |
8.64 |
7.43 |
7.21 |
8.65 |
6.99 |
8.40 |
9.66 |
| 6.87 |
7.89 |
9.79 |
6.85 |
7.62 |
7.44 |
8.55 |
8.70 |
| 7.00 |
8.80 |
9.30 |
8.03 |
7.33 |
8.58 |
9.88 |
9.94 |
| 6.39 |
7.54 |
|
|
7.14 |
9.14 |
|
|
Does this provide convincing evidence that space flight changes the
red blood cell mass of rats?
Answers
Rubric
- describe experimental design: 4 points
- state hypotheses: 4 points
- set up potential outcomes: 4 points
- calculate P-value using simulation: 4 points
- use normal approximation to calculate P-value or confidence interval: 4 points
- state conclusion: 4 points
Total: 24 points
Please see Canvas for a more detailed description of each rubric item.
Logistics
To be held during tutorial times, November 13-14. See your interview time here.