105.
Evaluate the following generalization(s), identifying sample, population, attribute of
interest, and the extent to which the claims involved are knowable. Consider carefully the
size and diversification of the sample and the extent to which the population differs or
may differ from the sample; remember, what’s important is that the sample be
representative.
NEW YORK (AP)—Women who read “bodice-rippers,” a sexy, violent genre of historical
romance novel, have sex 74 percent more often than nonreaders, according to a survey by
two psychologists from the Emory Medical School in Atlanta, who interviewed 72 middle-
class women in Atlanta, an equal number of them housewives, working women, and
college students. Women who read the romances reported making love an average of 3.04
times a week, compared to 1.75 for nonreaders.
Our concern here is whether the 3.04 and 1.75 times a week figures generalize from the
Atlanta sample. First, we’d not be at all surprised if there were an important discrepancy
between reports of frequency and actual frequency (the article runs the two together).
Further, a sampling of Atlanta women may not be representative of American women even
in regard to reporting the frequency of sex. There may be cultural differences between
urban and nonurban areas, southern and other areas of the country, and so forth, that
affect attitudes about sex and reports about sexual activity. Also, does the distribution in
the sample among housewives, working women, and college students reflect the
distribution in the population as a whole? Are one-third of American women college
students, for instance? Only if they were would this sample be representative.
106.
Evaluate the following generalization(s), identifying sample, population, attribute of
interest, and the extent to which the claims involved are knowable. Consider carefully the
size and diversification of the sample and the extent to which the population differs or
may differ from the sample; remember, what’s important is that the sample be
representative.
According to a study published by Dr. William P. Newman III of Louisiana State University
Medical Center in the
New England Journal of Medicine
, physicians in Bogalusa,
Louisiana, conducted autopsies on thirty-five youngsters ranging in age from seven to
twenty-four (the average age was eighteen) who had died mostly from accidents,
homicides, or suicides. They found that all but six of the young people had fatty streaks on
their aortas, the body’s main artery. Fatty streaks are the earliest gross recognizable
lesions of atherosclerosis (hardening of the arteries), according to Newman. Since there
was a direct link between the number of fatty streaks and the cholesterol levels in the
young people, Newman recommended that all schoolchildren be checked for high
cholesterol levels.
Newman is generalizing from the sample of thirty-five young people to all schoolchildren.
However, he probably would not say that the sample indicates that a majority of all young
people have the early signs of atherosclerosis. Rather, he would say that the sample
suggests that a sufficient number of young people may have that disease to make
monitoring the cholesterol levels of all children worthwhile. Interpreted this way, this is a
reasonable generalization: the Bogalusa study does warrant concern and further
investigation.
107.
Evaluate the following generalization(s), identifying sample, population, attribute of
interest, and the extent to which the claims involved are knowable. Consider carefully the
size and diversification of the sample and the extent to which the population differs or
may differ from the sample; remember, what’s important is that the sample be
representative.
Don’t buy any Australian wine. I’ve had Australian wine before and, believe me, you won’t
like it.
Well, maybe she will. This is too hasty. That one kind of Australian wine was not very good
doesn’t mean that there aren’t good varieties. Every country that makes wine makes at
least a little bad wine.
108.
Evaluate the following generalization(s), identifying sample, population, attribute of
interest, and the extent to which the claims involved are knowable. Consider carefully the
size and diversification of the sample and the extent to which the population differs or
may differ from the sample; remember, what’s important is that the sample be
representative.
Hamilton City was considering annexing a portion of land adjacent to the city limits where
construction of a subdivision was planned. To determine what the residents of the town
thought about this annexation and about municipal growth in general, the city council had
a poll taken. One thousand of the city’s fifteen thousand registered voters were randomly
selected and asked three questions: (1) Do you favor no growth, modest growth, or
accelerated growth for Hamilton City? (2) Do you favor annexation of the eight-hundred-
acre Osborne parcel north of town and its planned subdivision? (3) Should the city enter
into agreements with developers promising to supply city services, such as sewers and
street maintenance, in return for the added tax revenue the developer’s projects will
produce? The results of this survey were taken to be the “official” opinion of the voters of
Hamilton City.
There is clearly nothing wrong with the sample size, and, if the selection was indeed
random, this poll can be taken as a reliable indicator of what the voters of Hamilton City
think about the questions asked. The problem is the questions: The first is much too
vague (we’d bet the great majority of responses favored modest growth, whatever that
means); the second can be intelligently answered only by voters who understand the
implications of annexation—we can imagine a voter responding yes to the question and
109.
Evaluate the following generalization(s), identifying sample, population, attribute of
interest, and the extent to which the claims involved are knowable. Consider carefully the
size and diversification of the sample and the extent to which the population differs or
may differ from the sample; remember, what’s important is that the sample be
representative.
Mr. Smythe has closed each of the last four contracts with France International. Seems to
me he’d be likely to do well with the rest of our overseas deals.
This may be a biased sample. Did Mr. Smythe work with the same people on the four
France International contracts? More diversity in the sample would make this a stronger
argument.
110.
In evaluating the following generalization(s), identify sample, population, attribute of
interest, and the extent to which the claims involved are knowable. Consider carefully the
size and diversification of the sample and the extent to which the population differs or
may differ from the sample; remember, what’s important is that the sample be
representative.
A New York newspaper stopped theatergoers as they exited from a performance of
La
Tragédie de Carmen
and asked them whether they thought that Broadway theater was
better or worse than it was ten years ago. When the majority of the respondents answered
that they thought it was worse, the paper printed an article with the headline “Public
Thinks Broadway Is Going Downhill.” Does the poll justify the headline?
No. “Public” is misleading, since it could be taken to refer to the general public and not
just the theatergoing public. More important, the poll is highly biased in at least two ways:
it may be that the production mentioned does not draw a typical theater audience, and
hence the sample may be biased; and the effects of the performance attended may bias
an individual respondent (whether he liked this particular performance may have unduly
influenced his answer).
111.
Evaluate the following generalization(s), identifying sample, population, attribute of
interest, and the extent to which the claims involved are knowable. Consider carefully the
size and diversification of the sample and the extent to which the population differs or
may differ from the sample; remember, what’s important is that the sample be
representative.
Memo: “We interviewed Haddow and found that she could handle each of the problems
we gave her. I recommend we hire her.”
The speaker is betting that because Haddow can solve certain kinds of problems, she’ll be
able to solve all those she’s given. If the problems she solved really are representative of
the problems she will encounter, then it’s a good bet.
112.
In evaluating the following generalization(s), identify sample, population, attribute of
interest, and the extent to which the claims involved are knowable. Consider carefully the
size and diversification of the sample and the extent to which the population differs or
may differ from the sample; remember, what’s important is that the sample be
representative.
Readers of
Consumer Reports
can write in their opinions of movies they have seen. Each
month, CR reports the total number of opinion votes it receives in this way. In one issue,
the average rating of a certain movie is 4 on a scale of 1 to 5, with 5 the bad end of the
scale. The total vote on the movie is 107. How sound would a generalization from this
sample to American moviegoers in general be?
Not very. We know that maybe 107 people who know about the CR movie poll didn’t like
the movie very much (we say “maybe” because some may have voted more than once),
but that’s about all we know. There is no assurance that the sample is representative of
the population mentioned in the question.
113.
In evaluating the following generalization(s), identify sample, population, attribute of
interest, and the extent to which the claims involved are knowable. Consider carefully the
size and diversification of the sample and the extent to which the population differs or
may differ from the sample; remember, what’s important is that the sample be
representative.
“In a study done by a University of Pennsylvania psychologist, 29 suburban and 38 inner-
city children from the Philadelphia area, ranging in age from 3 to 12 years, were asked to
consume foods mixed with ‘disgusting’ substances, like apple juice stirred with a used
comb or containing a dead grasshopper. Almost two-thirds of the children from 3 to 6
sipped juice in which a grasshopper floated. There were no differences between city and
suburban children.” —Published in
Developmental Psychology
Would it be safe to say, on the basis of this study, that the same percentage of all
American children from ages three to six would be willing to sip juice in which a disgusting
object floats? Explain.
Your essay should clarify what the sample and population classes are and what
characteristic is attributed to each (note the shift from “apple juice in which a grasshopper
floats” to “juice in which a disgusting object floats”). Further, the essay should address
the “knowability” of the thesis, given the latter’s vagueness, and show that the writer
remembered the cautions in the chapter about making inferences in generalizing from a
sample. The essay should also consider the size, diversity, and representativeness of the
sample.
114.
Evaluate the following generalization(s), identifying sample, population, attribute of
interest, and the extent to which the claims involved are knowable. Consider carefully the
size and diversification of the sample and the extent to which the population differs or
may differ from the sample; remember, what’s important is that the sample be
representative.
Mónica is an excellent Spanish classical dancer. With a bit of practice, she’d probably be a
fine flamenco dancer as well.
This is not as good an argument as it might appear. Different art forms may be much more
different from one another than they might at first appear. Certainly we’d like Mónica’s
chances better than most people’s, but it’s by no means a sure thing.
115.
Critically discuss the following analogical argument:
Economic sanctions simply do not work. As a weapon of international persuasion, they are
about as effective as popguns.
The United Nations imposed drastic sanctions upon Rhodesia; they failed utterly.
We imposed sanctions upon Poland; nothing happened.
Our government has forbidden trade with Cuba for the past twenty-five years; Cuba goes
its own way. Most recently, the president has laid heavy sanctions upon Libya; our noble
allies have pooh-poohed the effort.
You can count on the same kind of result if economic sanctions are imposed on North
Korea.
We think that a good evaluation should identify the premise-analogue, the conclusion-
analogue, and the attribute of interest. The last of these is vague in this example—the
phrases “failed utterly,” “nothing happened,” and “goes its own way” are not clear. The
claim that “our noble allies pooh-poohed the effort” attributes a characteristic to the
Libyan case that is different from that attributed to the others. Is the author trying to say
that economic sanctions never have an effect whatsoever? His remarks don’t say so (Cuba
may “go its own way,” but American sanctions were very detrimental to the Cuban
economy). How knowable is such a claim? Does he mean that sanctions don’t destroy a
country? Are we talking about American sanctions or sanctions imposed by all of
America’s allies as well? Any relevant differences between North Korea and the other
countries mentioned would add to a critical evaluation.
11–72
116.
Read and discuss the following report. In your discussion, identify the experimental and
control groups, say whether there may be confounding variables in the study, and
determine what the outcome probably was. (What does “no statistically significant
difference” probably mean as it is used near the end of the report?)
“A report released today said that a small, controlled study found magnets were no more
effective than sham devices in treating chronic lower back pain.”
“But researchers note in the
Journal of the American Medical Association
that the negative
result from an experiment with just 20 patients doesn’t rule out the possibilities that
magnets can help lower back pain or that magnet therapy can really work.
Such therapy has gained enormous popularity in recent years, despite little scientific
evidence that the treatments work to relieve pain, improve circulation, or offer any other
health benefits.
Celebrities, scores of books, and hundreds of Web sites promote the treatments, even
though the Food and Drug Administration forbids any healing benefits to be claimed for
them. By some estimates, more than $5 billion worth of therapeutic magnets have been
sold worldwide.
A number of formal experiments, several supported by the National Institutes of Health,
are under way to test magnets on a variety of painful chronic conditions.
The latest study, carried out by Dr. Edward Collacott of the Veterans Affairs Medical
Center in Prescott, Arizona, and colleagues, is thought to be the first published experiment
to use active and inactive magnets for more than a single episode of treatment, and for
longer than 45 minutes.
All the patients in the study group had lower back pain, including the deformation of at
least one articulating part of a vertebra. They had experienced pain in the same area of
the back for an average of 19 years.
Each patient wore a flexible, rubberlike device for a total of six hours a day, three days a
week, for two weeks. Each used an active bipolar magnet and an identical-looking, de-
magnetized device for one week, but neither the patients nor the doctors treating them
knew which therapy was being used.
The patients were questioned about their pain using a standardized questionnaire for
pain measurement. Doctors also examined the patients more formally to determine the
range of motion in the lower spine.
At the end of the study, the researchers found ‘no statistically significant difference’
between patients when they’d been wearing the real magnets or shams.
Collacott and his coauthors said more studies should be done to verify their results.
This was a pilot study and was not intended to prove or disprove the effectiveness of
magnet therapy in general. Additional studies using different magnets, treatment times,
and patient populations are needed.”
—Scripps Howard News Service
Answers will vary
117.
“An FBI study of thirty-five serial killers [killers of several people, not all at once] revealed
that twenty-nine were attracted to pornography and incorporated it into their sexual
activity, which included serial rape and murder.” This assertion, taken from an
antipornography ad, seems to have been intended to show that pornography is a causal
factor of serial rape and murder. Does it show that?
An essay on this question should demonstrate sensitivity to the following points: The
assertion about the FBI study would support the causal claim in question only if the
frequency of attraction to pornography in the “experimental group” cited above were
known to exceed significantly the frequency in a “control group” of people who had not
committed serial rape and murder. Further, that condition, while necessary for the FBI
118.
According to Department of Transportation statistics for 2005: 1% of drivers received a
citation for a moving violation; 40% of them were under 30 years old. Which of the
following conclusions (about 2005) CANNOT be deduced from this information? Explain
your answer in no less than a half a page, and no more than one page.
1. 99% of drivers did not receive a citation for a moving violation.
2. 60% of those who received a citation for a moving violation were 30 or older.
3. 60% of those who did not receive a citation for a moving violation were under 30.
4. 60% of drivers under 30 years old received a citation for a moving violation.
5. A cousin who is under 30 is more likely to get a citation for a moving violation than is a
cousin who is 30 or older.
Conclusions (3), (4), and (5) cannot be deduced from the given information.
119.
Evaluate the following argument in accordance with the criteria discussed in the text.
Parker’s mimosa tree is getting yellow and dropping leaves. He figures it must be the tiny
little caterpillars he sees on it, since before he saw them the tree seemed fine.
Paired unusual events principle, and a reasonable conjecture; Parker probably would have
noticed the changes in the tree previously had they been due simply to a change of
season.
120.
Evaluate the following argument in accordance with the criteria discussed in the text.
Sharon has observed that her teacher sometimes seems to be in a bad mood and
speculates why. “Well,” she thinks, “it seems to happen only when people haven’t done
their assignments. That must be it.”
Common variable principle, though if this is the cause, then Sharon’s teacher may be in a
bad mood a lot of the time.
121.
Evaluate the following argument in accordance with the criteria discussed in the text.
Studies indicate that older women who attempt weight training seem to be in better shape
physically than those who don’t. This is a good reason for older women to lift weights.
Could be confusing cause and effect, from what’s said here. The claim has been
confirmed, however.
122.
Evaluate the following argument in accordance with the criteria discussed in the text.
Cheryl and her new acquaintance, Ted, have just walked into Target when she spots her
former boyfriend, Lemmy. “Oh, for crying out loud,” Cheryl thinks. “Why would he come
into Target, of all places? I’m sure I must be being punished for something I did.”
Cheryl is approximating some type of paired unusual events principle reasoning, but this is
probably just coincidence.
11–76
123.
Evaluate the following argument in accordance with the criteria discussed in the text.
“Four years ago, nonfat milk sold for 95 cents per half gallon. Today I paid $1.45 per half
gallon at one of our low-priced supermarkets. That’s a 52 percent increase in just four
years for an average of 13 percent per year, while the official government inflation rate is
less than 3 percent. Why is this? It’s not a coincidence that four years ago we got our first
Republican governor in this state in a long time.”
—From a newspaper call-in column
Post hoc
reasoning; it probably is a coincidence.
124.
Evaluate the following argument in accordance with the criteria discussed in the text.
See? When she has a good day at the store and sells lots of clothes, she always is in a
good mood. It just shows you how effective a good mood can be in the sales business. The
customer eats that stuff up.
Consider confusing cause and effect.
125.
Evaluate the following argument in accordance with the criteria discussed in the text.
Studies indicate that close to 85 percent of university professors are liberal Democrats. It
only stands to reason, therefore, that if you want to get a job as a college instructor,
register as a Democrat.
Could be an instance of ignoring a common, underlying cause (the same traits of mind that
are likely to get a person a job as a college instructor are also likely to make a person
favor the Democratic party); or, more likely, college professors tend to think their interests
are best served by the Democratic party, in which case we have confusing cause and
effect.
126.
Evaluate the following argument in accordance with the criteria discussed in the text.
February 2 is Groundhog Day. If the groundhog sees his shadow, there’ll be six more
weeks of winter. If he doesn’t, spring is right around the corner.
Groundhog Day claims are not causal: No one thinks the groundhog’s seeing or not seeing
his shadow causes whatever happens to the weather afterward. (A dark February 2 in
Pennsylvania—where Punxsutawney Phil, the official groundhog, lives—might be
correlated with an exceptionally short winter, for all we know. If it is, look for some sort of
meteorological phenomenon as a common cause.)
11–78
127.
Evaluate the following argument in accordance with the criteria discussed in the text.
Every time I play tennis my wrist hurts for several days afterward. If my doctor can’t help
me figure what to do about it, I may have to give up the game.
Common variable principle. Probably okay, although the likelihood is that tennis is only
part of the cause; some underlying condition is being exacerbated by playing tennis.
128.
Evaluate the following argument in accordance with the criteria discussed in the text.
A lottery winner, asked why he thought he had won a major prize, pulled a small
rhinestone four-leaf clover out of his pocket and said, “I think this had a lot to do with it.”
Post hoc
: “I carried my lucky charm, and I won.”
129.
Evaluate the following argument in accordance with the criteria discussed in the text.
My front door would creak every time I opened or shut it. I read in an old carpentry
publication that the way to fix the problem is tighten the hinges and grease the screws. I
did it, and it cured the problem.
Paired unusual events principle, and in this case just fine.
130.
Evaluate the following argument in accordance with the criteria discussed in the text.
I’d wash the car but for the fact that we don’t need any more rain.
This is probably best construed as a bad case of paired unusual events principle.
131.
Evaluate the following argument in accordance with the criteria discussed in the text.
The car usually makes it over the hills between here and the lake without any trouble. The
only time it makes any trouble is when we have to pull the boat and trailer; they must
make too heavy a load for the car’s small engine.
Common variable principle, although reading the first part of the second sentence as “The
car makes trouble if and only if the boat is pulled” allows a relevant-difference
interpretation as well. (That isn’t what the sentence says, but…)
132.
Evaluate the following argument in accordance with the criteria discussed in the text.
Before every voyage, we toss a drink to the old man in the sea.
That is, doing so brings good luck; not doing so brings bad luck. The superstition probably
originated as a faulty application of paired unusual events principle or common variable
principle, or both. (Before every airplane flight, your authors toss a drink down the hatch,
133.
Evaluate the following argument in accordance with the criteria discussed in the text.
“Of course he was outdoors Wednesday, Watson. That’s the only day there has been rain,
and he had a good bit of dried mud on the heels of his boots.”
Wednesday’s rain caused the mud to be on the boots: paired unusual events principle.
Note: Sherlock Holmes examples are as nice for the first part of this chapter as they are
for truth-functional inferences.
134.
Evaluate the following argument in accordance with the criteria discussed in the text.
“I’m over seventy years old and got all of my natural teeth but one. The secret is to eat a
dollop of raw veal bone marrow every day.”
—Attributed to Mrs. Keller [a “wise old woman of Ohio”] by Robert L. Tubbesing,
Old
Farmer’s Almanac
(1986)
This item is probably best analyzed as
cum hoc
. (I ate veal marrow every day and have all
my teeth save one; therefore, the former caused the latter). A case for common variable
principle can be made for this one, but not a very good case; there are too many other
possible variables.