HW Day 2. To hand in. [ ] marks additions to text question.
1.28, p. 28 Hispanic origins. Fig.
1.13 is a pie chart prepared by the
Census Bureau to show the origin
of the more than 43 million
Hispanics in the U.S. in 2006.
About what percent of Hispanics
are Mexican? Puerto Rican? You
see that it is hard to determine
numbers from a pie chart. Bar
graphs are much easier to use. (The
Census Bureau did include the
percents in the pie charts)
[Also: To argue with Moore: A
pie chart allows you to answer
easily questions like: "more than
half?", "About 2/3?" "Less than
1/4?",... "Less than 1/8?" Describe
these groups in those simple-fraction terms: Mexican, Puerto Rican, Other-Hispanic.]
1.29p.29 Spam ...Here is a compilation of the most common types
of [email] spam. Make two bar graphs of these percents, one with
bars ordered as in the table (alphabetically) and the other with bars
in order from tallest to shortest. Comparisons are easier if you order
the bars by height.
[Note the categories "come" in alphabetical order. Just make the
bargraphs by hand on ordinary paper. In order by size, it's called a
Pareto chart . Also: Calculate how much "other" spam there is, and
Use your pie template to make a pie chart. (The pie chart is only "legal"
Type of spam
Adult
Financial
Health
Internet
Leisure
Products
Scams
Percent
19
20
7
7
6
25
9
if every item falls into only one box. I wonder: is a Viagra ad Adult, Health, Leisure, or Products?]
1.40 p. 35 Marijuana and traffic accidents: Researchers in New Zealand interviewed .907
drivers aged 21. They had data on traffic accidents and they asked the drivers about marijuana
use. Here are data on the numbers of accidents caused by these drivers at age 19, broken down
by marijuana use at the same age.
marijuana use per year
Never 1-10
11-50 51+
a) Explain carefully why a useful graph must
compare rates (accidents per driver) rather
times
times
times
than counts of accidents in the four marijuana
Drivers
452
229
70
156
use classes.
Accidents 59
36
15
50
caused
b) Make a graph that displays the accident
raste for each class. What do you conclude? (You can’t conclude that MJ use causes accidents,
because risk takers are more likely both to drive aggressively and to use marijuana.
[Divide accidents by # of drivers to get rates. Also: This table has been summarized from a
dataset where the Individuals were the 907 drivers interviewed, and the Variables were
Marijuana Use during 19th year and Accidents Caused during 19th year. (The drivers were then
put into categories by Marijuana Use and the accidents totaled in each category). As presented,
Marijuana Use is a Categorical variable. Is it Nominal, or Ordinal?]
2.15, p. 58 Here are the amounts of money (cents) in coins carried by 10 students in a statistics
class. 50 35 0 97 76 0 0 87 23 65.
From this dataset (coins), make a Dotplot. Is there anything odd/interesting about the data set?
Don't do anything else.
1.9,p.18 Unmarried women.
Fig. 1.9 shows the distribution of
the state %s of women aged 15
and over who have never been
married.
a) the main body of the dist. is
slightly skewed to the right.
There is one clear outlier, the
District of Columbia. Why is it
not surprising that the % of
never-married women in higher
in DC than in the 50 states?
b) The midpoint of the
distribution is the 26th state in
order of percent of never-married
women. In what class does the
midpoint fall? [Add up bars left
to right till you’ve got
“enough”]. About what is the
spread (smallest to largest) of the
dist.
1.30 fruit ... Many of us
don’t eat enough [fruit]. Fig.
1.14 is a histogram of the
number of servings of fruit
per day claimed by 74
seventeen year old girls in a
study in PA. Describe the
shape, center, and spread of
the dist. What percent of
these girls ate fewer than 2
servings per day?
1.32 p. 29 Returns on common stocks. The return on a stock is the change in its market price
plus any dividend payments made. Total return is usually expressed as a percent of the
beginning price. Fig. 1.16 is a histo of the dist. of the monthly returns for all stocks listed on
U.S. Markets from Jan 1985 to Sept 2007 (273 months) The extreme low outlier is the market
crash of Oct. 1987, when stocks lost 23% of their value in one month.
a) Ignoring the outliers, describe the overall shape of the distrib. of monthly returns.
b) What is the
approx. center of this
distribution? (for
now take the center
to be the value with
roughly half the
months having lower
returns and half
having higher
returns.)
c) Approx. what
were the smallest and
largest monthly
returns, leaving out
the outliers? (This is
one way to describe
the spread of the
distribution)
d) A return less than
zero means that
stocks lost value in
that month. About
what percent of months had returns less than zero?
-------1.31, p. 29 IQ [reading stemplot] Fig. 1.15 is a
stemplot of the IQ test scores of 79 seventhgrade students in a rural Midwestern school.
a) Four students had low scores that might be
considered outliers. Ignoring these, describe the
shape, center, and spread of the distribution.
(Notice that it looks roughly bell-shaped.)
b) We often read that IQ scores for large
populations are centered at 100. What percent
of these 78 students have scores above 100?
p. 32, 1.35 doctors. [Do a stemplot, not a histogram. Use hundreds as stems (tens as leaves),
and split them as on p. 22. The tallying and the effect is the same as a histogram with classes
150-199, 200-249, 250-299, etc.]
Table 1.5 gives the number of active medical doctors per 100,000 people in each state.
a) Why is the number of doctors per 100,000 people a better measure of the availability of health
care than a simple count of the number of doctors in a state?
b) Make a histogram stemplot that displays the distribution of doctors per 100,000 people. Write
a brief description of the distrib. Are there any outliers? If so, can you explain them? [I’m not
sure the answer book’s explanation is complete!]
Women
Men
1.38 p. 35 Study times
120
180
360
240
90
120
30
90
We asked the students in a 180
120
180
120
240
170
90
45
30
120
large first-year college
150
120
180
180
150
150
120
60
240
class how many minutes
200
150
180
150
180
240
60
120
60
they studied on a typical
120
60
120
180
180
30
230
120
95
90
240
180
115
120
0
200
120
120
weeknight. Here are the
responses of random samples of 30 women and 30 men from the class:
a) Examine the data. Why are you not surprised that most responses are multiples of 10
minutes? We eliminated one student who claimed to study 30,000 minutes per night. Are there
any other responses you consider suspicious?
[continued]
200
75
300
30
150
180
(study times, continued)
b) Make a back-to-back stemplot to compare the two samples. That is, use one set of stems with
two sets of leaves, one to the right and one to the left of the stems. (Draw a line on either side of
the stems to separate stems and leaves.) Order both sets of leaves from smallest at the stem to
largest away from the stem. Report the approximate midpoints of both groups. Does it appear
that women study more than men (or at least claim that they do?)
[You can do back to back, or do side by side on the same scale, like fig. 2.5, p. 57. Using
hundreds as stems only gives 3 stems. Splitting by 5's (p. 22) might be good enough. Notice the
mental rounding of the responses, to quarter hours if not to ten minuteses. Makes "Granular"
data.]
1.43, p.36, Housing starts Timeplot. Fig. 1.18 is a time plot of the number of single family
homes started by builders each month from Jan. 1990 to Dec. 2007. The counts are in thousands
of homes.
a) The most notable pattern in this time plot is yearly up-and-down cycles. At what season of the
year are housing starts highest? Lowest? The cycles are explained by the weather in the
northern part of the country.
b) Is there a longer-term trend visible in addition to the cycles? If so, describe it.
c) The big economic news of 2007 was a severe downturn in housing that began in mid-2006.
How is this downturn visible in the time plot?