Watson-Glaser Critical Thinking Appraisal Evaluating Causal Relationships 4 — Questions and Answers
Question 1: A city installs more streetlights in high-crime neighborhoods, and crime drops by 20% over the next year. A resident concludes that the streetlights caused the crime reduction. Which alternative explanation most weakens this causal claim?
- The city also increased police patrols in those neighborhoods during the same period. (Correct answer)
- Streetlights are expensive to maintain and operate.
- Crime rates fluctuate naturally from year to year.
- Residents feel safer when streets are well-lit.
Correct answer: The city also increased police patrols in those neighborhoods during the same period.
A concurrent intervention (increased patrols) is a confounding variable that could independently explain the crime reduction, undermining the streetlight-as-cause claim.
Question 2: Which of the following best describes the logical fallacy 'post hoc ergo propter hoc'?
- Assuming that because two events are correlated, one must cause the other.
- Assuming that because one event followed another, the first caused the second. (Correct answer)
- Concluding that a cause is invalid because its effect is undesirable.
- Overgeneralizing from a single case to a universal causal law.
Correct answer: Assuming that because one event followed another, the first caused the second.
'Post hoc ergo propter hoc' means 'after this, therefore because of this'—incorrectly inferring causation from temporal sequence alone.
Question 3: Researchers find that people who eat breakfast regularly have higher academic performance. A school mandates breakfast for all students. Which assumption is necessary for this policy to achieve its goal?
- Breakfast programs are cost-effective compared to other interventions.
- The correlation between breakfast and performance reflects a causal relationship. (Correct answer)
- Students who skip breakfast do so intentionally.
- Academic performance is the only metric worth improving.
Correct answer: The correlation between breakfast and performance reflects a causal relationship.
The policy only works if eating breakfast actually causes better performance, not merely if it correlates with it (e.g., via a third factor like household stability).
Question 4: A study shows that hospitals with more nurses per patient have lower patient mortality rates. An administrator concludes: 'Hiring more nurses will reduce deaths.' What is the strongest challenge to this conclusion?
- Nurses are costly and may strain the hospital budget.
- Better-funded hospitals may both hire more nurses and have other quality advantages that reduce mortality. (Correct answer)
- Mortality rates vary by the type of illness being treated.
- Some nurses are more experienced than others.
Correct answer: Better-funded hospitals may both hire more nurses and have other quality advantages that reduce mortality.
Reverse causation or a shared underlying cause (hospital funding/quality) could explain the correlation without nurse staffing being the direct cause.
Question 5: In Watson-Glaser reasoning, which of the following scenarios demonstrates a 'necessary cause' rather than a 'sufficient cause'?
- Striking a match is enough on its own to start a fire.
- Oxygen must be present for a fire to burn, but oxygen alone does not start a fire. (Correct answer)
- Heavy rain always causes flooding in this valley.
- Studying guarantees a passing score on this exam.
Correct answer: Oxygen must be present for a fire to burn, but oxygen alone does not start a fire.
A necessary cause must be present for the effect to occur but does not guarantee it; oxygen is required for fire but alone cannot produce it.
Question 6: Teen smartphone ownership increased dramatically at the same time teen anxiety rates rose. A commentator declares smartphones are causing teen anxiety. Which evidence would most SUPPORT (rather than undermine) this causal claim?
- An experiment in which randomly selected teens who reduced screen time showed measurable anxiety decreases compared to a control group. (Correct answer)
- A survey showing that anxious teens report using phones more than calm teens.
- News articles about teens feeling addicted to social media.
- Statistics showing that both trends began in the same year.
Correct answer: An experiment in which randomly selected teens who reduced screen time showed measurable anxiety decreases compared to a control group.
A randomized controlled experiment that manipulates the proposed cause and observes the effect provides the strongest evidence for causation.
Question 7: A farmer notices that fields treated with a new fertilizer yield 30% more crops. He concludes the fertilizer caused the increase. Which factor would most threaten this conclusion if true?
- The fertilizer was applied in a different season than usual.
- The treated fields happened to receive significantly more rainfall than the untreated fields that year. (Correct answer)
- The fertilizer contains chemicals that some consumers prefer to avoid.
- Other farmers in the region did not use the same fertilizer.
Correct answer: The treated fields happened to receive significantly more rainfall than the untreated fields that year.
If treated and untreated fields had different rainfall, rainfall—not the fertilizer—could be the true cause of the yield difference.
Watson-Glaser Critical Thinking Appraisal Evaluating Causal Relationships 4
A city installs more streetlights in high-crime neighborhoods, and crime drops by 20% over the next year.
A resident concludes that the streetlights caused the crime reduction.
Which alternative explanation most weakens this causal claim?