Chapter 8 Answer Key to Select Chapter Exercises

Exercise 8.1
2. Target group: the water of Lake Winnipeg; Sample: one hundred and fifty samples of water taken from different sites all along the shoreline of Lake Winnipeg; Relevant property: level of toxic chemicals.
The argument is strong.
5. Target group: people in Canada; Sample: an unknown number of adults in Toronto and Montreal; Relevant property: favouring banning construction of new oil pipelines.
The argument is weak; the sample is not representative.
7. Target group: Canadians; Sample: 900 randomly-selected pet owners; Relevant property: opinion on allowing the slaughter of dogs for food.
The argument is weak because the sample is not likely to be representative. The opinions of pet owners on this topic may not reflect the opinions of Canadians more generally.
9. Target group: injuries to swimmers at beaches everywhere; Sample: some number of newspaper stories; Relevant property: involvement of sharks in injuries to swimmers.
The argument is weak because the sample is not likely to be representative. (Injuries attributable to sharks are more likely to generate news stories than injuries attributable to beach volleyball, or sunburn, etc.).

Exercise 8.2
2. Strong. To make this into a weak argument, a smaller number of samples could be taken, all at one location.
5. Weak. To ensure a strong argument, discard the very unrepresentative sample of people from big cities and conduct a random poll of people from across the country.
7. Weak. To ensure a strong argument, include a wider range of Canadians in the survey (including ones who do not own pets).
9. Weak. The argument would be stronger if the sample included all sources of injury at beaches, not just those sensational enough to be reported in newspapers.

Exercise 8.3
2. The poll does not support the pollsters’ conclusions. This is a biased sample. Only nurses were surveyed, and they have a personal stake in the question.
5. The survey does not support the conclusion. Although we do not know the exact sample size, “a number” of classrooms is not a large sample. Also, there is a worry that such a process would not have made students feel free to speak up.

Exercise 8.4
2. c
4. c

Exercise 8.5
2. Slightly more likely to be true. The revised sample, however, is still biased because it consists of nurses and of other health professionals who are likely especially sympathetic to the interests of nurses.
5. More likely to be true.

Exercise 8.6
2. Individual: Your “lucky number” ticket; Group: all tickets in that particular lottery; Characteristic: likelihood of being the winning ticket; Proportion: 1 in 1,000,000.
3. Individual: Jessica; Group: Canada’s population; Characteristic: having an annual net income of more than $191,000; Proportion: 1 in 100.

Exercise 8.7
3. Non-typical individual (Oprah is well-known to have a very successful business empire, so her business is far from typical)
5. Unacceptable premise (shark attacks are actually very rare)

Exercise 8.8
3. Enumerative induction.
6. Argument by analogy. One instance compared: A bully and a dictator; Relevant similarities: Tolerating a bully or a dictator leads to further abuse; Conclusion: The best course of action for people oppressed by a dictator is to resist and attack.
The argument is weak because dictators rarely surrender simply because there is violent resistance to their rule.
8. Literary analogy.
10. Argument by analogy. Two things being compared; Relevant similarity: having one or a few things that are thought to power or drive it; Conclusion (unstated): “Cutting the deficit by gutting our investments in innovation and education is a bad idea.”
The argument is weak. There are many relevant dissimilarities between an airplane and an economy.

Exercise 8.9
2. Things being compared: liking various restaurants; Relevant similarities: geographical origins; Diversity among multiple cases: a somewhat significant factor because the quality of restaurants varies so much; Conclusion: I’m not likely to like any other South American restaurants.
The argument is weak. Restaurants vary in quality along many dimensions. The training and experience of the kitchen staff, for instance, may matter more than the geographical region that the restaurants represent.
3. Things being compared: Development of a person and of the human race; Relevant similarities: Both involve biological processes of great complexity taking place under “appropriate conditions” and commencing with a single cell; Diversity among multiple cases not a significant factor; Conclusion: Under appropriate conditions, a cell may, in the course of untold millions of years, give rise to the human race.
The argument is strong.
7. Things being compared: pregnancy and involuntarily being “plugged into” a famous violinist; Relevant similarities: the situation may be unplanned, the fetus or violinist will die if “disconnected,” staying connected may involve hardship; Diversity among multiple cases not a significant factor; Conclusion: it is morally justified for a woman to abort.
The argument is weak because there are significant unmentioned differences.

Exercise 8.10
1. Conclusion: B caused E. Joint method of agreement and difference. The argument is strong.
3. Conclusion: Police don’t care about black lives. Method of difference. The argument is relatively weak as it stands. It’s not clear whether the evidence is merely anecdotal, or based on real statistics. Also, various factors – other than caring – affect response times, including traffic patterns, location of police stations, and so on.
5. Conclusion: (unstated) Several aspects of the students’ behaviour resulted in COVID-19. Method of agreement. The argument is strong.
8. Conclusion: Oranges and lemons were the most effective remedies for the illness. Joint method of agreement and difference. The argument is strong.
11. Conclusion: There’s a causal connection between serum cholesterol levels and risk of atherosclerosis. Correlation. The argument is strong.
14. Conclusion: The growth of Lissuin depends on the correct amount of rainfall (more specifically, too much rain causes the flowers to grow poorly). Method of difference. The argument is relatively strong, although we would need to rule out other possible causes.
15. Conclusion: Being in this building interferes with my phone reception. Method of difference. The argument is strong.
20. Conclusion: Barry’s criminal behaviour is caused by high outdoor temperatures. Correlation. The argument is weak.

Exercise 8.11
1. (a) Misidentifying or overlooking relevant factors.
3. (a) Misidentifying or overlooking relevant factors.
5. (a) Misidentifying or overlooking relevant factors.
8. (b) Being misled by coincidence; (c) falling for the post hoc fallacy.
11. (a) Misidentifying or overlooking relevant factors.
14. (a) Misidentifying or overlooking relevant factors; (b) being misled by coincidence.
15. (a) Misidentifying or overlooking relevant factors; (b) being misled by coincidence.
20. (a) Misidentifying or overlooking relevant factors; (b) being misled by coincidence.

Exercise 8.12
3. (b) A sufficient condition
5. (d) Neither a necessary nor a sufficient condition
8. (b) A sufficient condition
10. (c) A necessary and sufficient condition