ACTIVITY 1
 Solutions
1.1
Suppose a medical researcher compares the average blood pressures of women who take oral
contraceptives to the blood pressures of women who do not.
a.
Is blood pressure a categorical variable or a quantitative variable?
Quantitative; we would measure blood pressure.
If we categorized the values (e.g. low, medium, high)
then this would be a categorical variable.
b.
Is oral contraceptive use (or not) a categorical variable or a quantitative variable?
Categorical; data produced from yes/no questions are categorical.
c.
What variables that affect blood pressure might confuse the comparison of average blood pressures for
users and nonusers? That is, what factors affecting blood pressure might differ for users and nonusers.
Explain.
Answers will vary. One possibility is age. Age affects blood pressure and also there may age differences
between users and nonusers of oral contraceptives.
1.2
A statistics class at UC Davis was asked “About how many hours do you watch television per week?
A fivenumber summary of the responses from 173 students follows.
Median
6
Quartiles
2
12.5
Extremes
0
100
a.
What were the median hours of weekly television watching?
In the context of this situation, write a
sentence that interprets the median.
Median = 6. About 50% of the class watched 6 or less hours per week.
b.
Give the value that completes the following sentence.
About 1/4 of the students watch less than ___
hours of television per week.
2 (lower quartile, Q1) since Q1 represents the first quartile which is the value where 25% of the data falls
at or below.
c.
Give the value that completes the following sentence.
About 1/4 of the students watch more than ___
hours of television per week.
12.5 (upper quartile, Q3) since Q3 represents the third quartile which is the value where 75% of the data
falls at or below, and conversely 25% watch at or above.
d.
What is an interval that describes the middle 1/2 of the student’s television watching amounts?
2 to 12.5
(between the quartiles Q1 and Q3)
e.
The
mean
for these data is 8.9 hours per week.
How do you think the mean is calculated?
Sum of all values divided by total number of values
Why do you think it is larger than the median in this instance?
There might be an outlier(s)
1
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In ANGEL on the Lessons page, access the Datasets folder. Within this folder, click on the link for
the data set named
U.S. Smoking (Minitab file)
. This should cause a program named Minitab to open,
with the data in place. The data are estimates of the percentage of adults who smoke in each state of the
U.S. (and also District of Columbia).
a.
In Minitab, use
Graph>StemandLeaf
to create a stemplot of the percents that smoke in the 50 states
and Washington D.C. In the dialog box, double click on the name of the second column to enter it as the
variable you want to plot.
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 '08
 BARROSO,JOAOR
 Statistics, Standard Deviation, Descriptive statistics

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