Stat 104 – Homework 3
Due Thursday September 19, 2013
Reading:
September 10 – September 19
September 24 – October 1
Chapter 3
Chapter 4
Assignment:
1. Complete the following problems from the text:
3.1 Which is the response/explanatory variable?
a.
b.
c.
3.5 Alcohol and college students.
a.
b.
c.
d.
e.
3.11 Used cars and the direction of association.
a.
b.
c.
d.
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2. Public opinion surveys are often conducted over the telephone. Until recently, people
conducting surveys contacted only landline telephones because including cell phones
in their samples would add significantly to the cost and difficulty of conducting the
surveys. Excluding cell phones could bias the results of surveys if characteristics of
cell phone users are different from those who have landline telephones. Below is a
summary of phone ownership and age for 982 adults in the United States. We wish to
see if age can explain some of the variability in phone ownership.
Age (years)
18 – 29
30 – 49
50 – 64
65 +
Total
Landline
only
54
200
262
239
755
Cell phone
only
94
87
37
9
227
Total
148
287
299
248
982
a) What proportion of the sample has cell phones only?
b) Compute row percentages for landline and cell phone owners, conditional
proportions, given the various age categories.
c) On the next page is a mosaic plot depicting the percentages calculated in b). Use
the percentages from b) and the mosaic plot to compare the age categories in
terms of their phone ownership. Your comparison should be written in complete
sentences and refer specifically to the percentages and the mosaic plot.
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Mosaic Plot
3. A good bottle of Bordeaux, a red wine from the Bordeaux region of France, can cost a
lot of money. Publications, like The Wine Spectator, rate wines with higher ratings
indicating better quality wine. We wish to investigate the relationship between the
cost of a bottle of Bordeaux and the rating. Below are Price ($) and Rating (on a
scale from 0 to 100) for 12 bottles of Bordeaux wine from the 2008 vintage.
Price ($)
20
15
11
90
66
50
Rating
89
87
86
91
90
89
Price ($)
40
16
22
43
30
161
Rating
88
88
87
90
89
91
a) Plot the data. Use Price ($) as the explanatory variable, x, and Rating as the
response, y. Describe the relationship between Price and Rating.
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b) Compute the mean and standard deviation for the Price ($). Round final answers
to 4 decimal places.
c) Compute the mean and standard deviation for the Rating. Round final answers to
4 decimal places.
d) Using   x  x  y  y   589.0 , compute the correlation between Price ($) and
Rating. Round final answer to 4 decimal places. Explain in words what this
correlation means.
4. We often read or hear reports about the relationship between diet and health. Data
were collected on the fat intake (grams per day per capita) and the death rate (number
of deaths per 100,000 people) from colon cancer for 30 nations. The data are
available on Blackboard Learn.
Use Analyze – Distribution in JMP to create graphical displays and numerical
summaries of the death rate data. The histogram should be oriented so that death rate
is along the horizontal axis. The intervals for death rate should go from 0 to 28 with
an increment of 4 and no minor ticks. The histogram should have a vertical axis with
a scale and label. Be sure to attach the JMP output to your assignment. Use the JMP
output to fully describe the distribution of death rates for the 30 nations. Write your
description in complete sentences and be sure to refer specifically to the graphical and
numerical summaries.
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