Stat 240 Dec. 3 Lab Activities
Activity 1 (Work together!)
At the course website (www.stat.psu.edu/~rho/240/), near the bottom of the home page, there is a link
to a dataset named oldfaithful.txt. Link to this dataset, then copy and paste the data to a Minitab
worksheet.
The data are for n = 222 eruptions of the Old Faithful geyser in Yellowstone Park. The geyser erupts
every 70  30 minutes.
Variables are Duration = duration of the eruption (minutes) and TimeToNext = time (minutes) until
the next eruption. We’ll predict y = TimeToNext using x = Duration. That is, given the duration of
a geyser eruption, how long will it be until the next eruption?
A. Plot TimeToNext versus Duration. (Use Graph>Plot). Does the pattern appear to be linear? Is
the correlation positive, negative, or near 0?
B. Use Stat>Regression>Regression to find the regression equation for predicting TimeToNext (the
response) using Duration (the predictor). What is the equation?
C. Use the equation found in the previous part to predict TimeToNext (time to the next eruption) after
an eruption with Duration = 2 minutes
Suppose that after an eruption of Duration = 2, the time to next eruption is 56 minutes. What would
be the value of the prediction error (also called residual) for this observation?
D. In the output, what is the evidence that the observed relationship is “statistically significant?”
Give a p-value, describe, where you find this p-value on the output, and indicate what null hypothesis
is being rejected?
E. In Minitab, return to Stat>Regression>Regression, use the Options button. IN the box labeled
“Prediction intervals for new values,” enter 4. This will cause Minitab to create a 95% prediction
interval for the time to next eruption after an eruption that’s 4 minutes long. Click OK enough times
to get the output.
What is the predicted (single) value of TimeToNext for Duration = 4? (it will be on the output as
“Fit”)
What is the “95% PI” given in the output?
F. The output includes the information “S = 6.139.” As discussed in Monday’s class, this is the
standard deviation of y-values from the regression line. By doing the calculations, verify that the 95%
PI is approximately Predicted value  2 S.
Activity 1 continued:
G. The data are sorted by the values of Duration. In the Minitab worksheet, find the observations
with Duration = 4 minutes.
How many observations have Duration = 4?
How many of these observations have a value for TimeToNext not within the interval found in the
previous two parts?
Explain why this (fraction of observations not in the interval) is about what be expected for a 95%
prediction interval.
H. Refer back to part F. What is an approximate 68% prediction interval for values of TimeToNext
when Duration = 4?
Activity 2: Work together to form answers for sheet of practice questions distributed in class
Monday. The same questions are the next page of this handout as well.
Stat 240 Practice Questions
For each of the following problems, identify the statistical procedure that can be used to answer the
research question. For each question, give the number of your choice using the following numbered
list of choices.
1. 1-sample t-test of
H0: 
2. 1-sample t-interval
for 
3. 1 proportion Z-test
of H0: p= ...
4. 1 proportion Zinterval for p
Analysis Choices
5. 2-sample t-test of H0:
9. Paired t-test of d = 0
12 = 0
6. 2-sample t-interval for
10. Paired t-interval for d
12
7. 2-proportions Z-test of H0:
11. Regression
p1p2=0
8. 2-proportions Z-interval
for p1p2
1. What proportion of adults in the United States are in favor of the death penalty for persons
convicted of murder?
2. Is there a difference between the mean systolic blood pressures of women who use oral
contraceptives and women who do not?
3. Thirty individuals are timed to see how long it takes them to complete a manual dexterity task
both before and after drinking alcohol. How much difference is there in the mean times
needed to complete the task?
4. What is an equation that can be used to predict college GPA using high school GPA?
5. Are more than 50% of pregnant women able to correctly predict the sex of their babies?
6. What is the mean weight of six-year-old children?
7. Does the average amount of time spent studying differ for males and females?
8. Tread wear is measured in millimeters of tread remaining after 30,000 miles. Thirty cars are
selected for the experiment. On each car, one Goodyear tire and one Firestone tire is placed
randomly in one of two front positions. Is there a difference between the mean tread wear of
the two brands?
9. Is the proportion of men who experience sleep apnea (irregular breathing during sleep) higher
than the proportion of women who do?
10. What is the mean number of hours per week that Penn State students study?
11. Is mean normal human body temperature less than 98.6?
12. How much difference is there in the proportions of college men who have a tattoo and college
women who have a tattoo?
13. What is the relationship between the adult height of a son and the height of his father?
14. Is there a difference in the mean pulse rate of women and the mean pulse rate of men?
15. How much difference is there in the mean heights of 13-year old boys and 15-year old boys?
The data are from n=20 13-year olds and n=24 15-year olds How would the answer change
if the data were from a sample of n=30 boys all of whom had heights measured when they
were 13 years old and again when they were 15 years old.
16. In a survey done by a car manufacturer, people are asked which color they would pick for a
new car if the car was available in silver, blue, and green. Will more than 1/3 of all people
people pick silver?
17. Refer to the previous problem. What proportion will pick blue?
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