Question 48·Hard·Command of Evidence
At a busy university cafeteria, environmental economists Chen and Malik added labels to each hot-food menu item indicating the item’s estimated greenhouse-gas emissions, expressed in kilograms of equivalent (kg CO₂e). Over the next four weeks, sales of beef-based dishes fell by 23 percent, while sales of vegetarian alternatives rose by 17 percent. Chen and Malik contend that the labels changed purchasing behavior chiefly because diners wished to signal environmental responsibility to people around them, not because the labels altered diners’ perceptions of price, nutrition, or taste.
Which finding, if true, would most directly support Chen and Malik’s contention?
For “Which finding would most support the claim?” questions, start by carefully restating the claim and identifying its key cause-and-effect idea (here, that the labels changed behavior mainly due to social signaling, not altered beliefs about price, nutrition, or taste). Then ask yourself: What kind of new evidence would clearly show that this specific cause is at work? Look for answers that directly test or isolate that mechanism—often by comparing two situations that differ only in the factor the claim focuses on (such as public vs. private choices), while keeping other things the same. Eliminate options that merely provide background, rule out some alternative causes without confirming the proposed one, or shift to a related but different topic.
Hints
Clarify the researchers’ explanation
Before looking at the choices, restate in your own words what Chen and Malik think is the main reason the labels changed what people bought. Is it about private beliefs (price, nutrition, taste) or about what others see?
Think about public vs. private choices
If the labels mainly work because people want to signal something to others, what should happen when people make their choices where no one else can see them?
Look for an experiment that changes visibility, not the labels
Scan the options for a situation where the labels are the same, but the social setting of the purchase—whether others can see the choice—changes. Which choice most clearly tests that difference?
Step-by-step Explanation
Restate Chen and Malik’s contention
First, put the economists’ idea into your own words.
They are claiming why the emissions labels changed what people bought:
- Main cause they propose: Diners wanted to look environmentally responsible in front of other people (social signaling).
- Causes they reject: The labels did not mainly change how diners thought about price, nutrition, or taste.
So the question is asking: Which finding would most directly support the idea that the effect came from wanting to impress others, not from seeing the food differently in terms of cost, health, or flavor?
Decide what strong supporting evidence would look like
To support a “social signaling” explanation, you want evidence that:
- The same labels have a big effect when choices are visible to others, but
- Have little or no effect when choices are private (no one to impress).
That pattern would show that the labels change behavior mainly when there is an audience, which fits the idea of wanting to signal environmental responsibility. Evidence that only rules out price or nutrition changes is helpful, but it doesn’t by itself prove that social signaling is the main reason.
Eliminate choices that don’t test social signaling
Now look at the answer choices that clearly do not test whether visibility to others matters.
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Choice A (prices and portions stayed the same): This tells you the cafeteria didn’t change price or portion size, so those can’t explain the sales shift. But it doesn’t show whether the labels worked because of social signaling or because people privately cared more about emissions, health, or taste. It rules out some alternatives but doesn’t point to social signaling.
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Choice B (post-experiment taste and fullness ratings): This focuses on how tasty and filling diners think vegetarian vs. beef dishes are. That’s about taste and satisfaction, not about being seen by others. Depending on how you interpret it, it could even suggest perceptions did change, which goes against Chen and Malik’s claim. It doesn’t connect the labels’ effect to public image.
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Choice D (sodium-content labels change sales a little): This compares a different kind of label (sodium) and a different outcome size (5% change). It doesn’t tell you whether emissions labels worked because of being seen by others or because people truly cared more about emissions. It’s about what is labeled, not about whether choices are public or private.
Identify the choice that directly tests public vs. private decisions
The remaining option describes a second trial where customers pre-ordered meals privately through a smartphone app and then picked them up later, and adding the same emissions labels in this private setting produced almost no change in what people bought.
This is exactly the pattern that supports Chen and Malik’s contention: when choices are public (cafeteria line), labels strongly shift behavior; when choices are private (smartphone app), the labels barely matter. That means the labels’ effect depends on having an audience, which fits the idea that diners wanted to signal environmental responsibility to people around them.
Therefore, the correct answer is: “In a subsequent trial in which customers pre-ordered meals privately through a smartphone app for later pickup, adding the same emission labels produced almost no change in purchasing patterns.”