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Question

Difficulty: MediumStrengthen

To reduce light pollution, several rural resort towns recently replaced conventional globe streetlights with full-cutoff fixtures, which direct all emitted light downward. Over the two years following the replacement, evening retail sales in the commercial centers of these towns rose by 14 percent, while evening sales in neighboring towns that retained conventional lighting remained unchanged. Researchers concluded that the clearer view of the night sky created by the reduced upward glare made evening strolls through commercial districts more attractive to visitors, leading to increased retail spending. Which of the following, if true, most strongly supports the researchers' conclusion?

  1. A
    Surveys indicated that shoppers in the towns with new fixtures frequently reported feeling safer walking at night because the downward-directed light illuminated sidewalks more brightly than the old fixtures did.
  2. B
    The neighboring towns that retained conventional streetlights experienced a modest increase in municipal maintenance costs associated with streetlight bulb replacement.
  3. In the towns that installed the full-cutoff fixtures, the increase in evening retail sales occurred almost entirely on clear nights rather than on overcast nights when the stars were obscured.Answer
  4. D
    Every tourist who visits rural resort towns considers clear night skies to be the single most important factor when choosing vacation destinations.
  5. E
    Retail business owners in the neighboring towns were initially unaware of the lighting modifications implemented in the adjacent resort communities.

Answer

The statement showing that the increase in evening retail sales in the towns with new fixtures was concentrated on clear nights rather than overcast nights.
The correct response provides strong empirical support for the causal hypothesis by demonstrating covariation between the purported cause and the observed effect. If the sales increase occurred almost exclusively when the night sky was actually visible (clear nights) and disappeared when the view was blocked by clouds (overcast nights), it directly confirms that the aesthetic enjoyment of the night sky—rather than some constant feature like fixture shape or everyday downward lighting—was the operative factor behind the retail growth.

Step-by-Step Solution

1
Identify the premises and conclusion of the argument.
Premise: Replacing globe lights with full-cutoff fixtures correlated with a 14% increase in evening retail sales, while towns without the change saw flat sales. Conclusion: The improved visibility of the night sky caused visitors to find evening strolls more attractive, which drove the retail spending increase.
Isolating the conclusion reveals that the core reasoning relies on a specific causal attribution.
2
Identify the logical vulnerability or unstated gap in the causal claim.
The author assumes that night sky visibility itself caused the spending increase, rather than other factors associated with the fixture change (e.g., ground illumination, general economic shifts, or safety improvements).
Strengthening a causal argument requires corroborating the proposed mechanism, showing covariation, or ruling out alternative causes.
3
Evaluate the answer choices for evidence that strengthens the link between night sky visibility and retail spending.
Showing that the sales surge occurred specifically on clear nights (when the night sky was visible) and not on overcast nights (when the night sky was blocked) confirms that the effect is tied to the proposed cause.
Demonstrating that the effect is present when the cause is present and absent when the cause is absent directly reinforces causal validity.

Key Concept

Causal Strengthening via Covariation (Presence/Absence of Cause and Effect)
Estimated Time:1m 15s
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