Question 89·Medium·Inferences
To curb swarms of insects around streetlights, a city compared amber LED fixtures with blue-white LED fixtures over several weeks. On most nights, observers counted fewer insects around the amber lights. A city official argued that the results show amber lights attract fewer insects and should therefore replace the blue-white ones. Entomologist Dr. Ruiz disagrees. He notes that on moonless nights the two types of lights drew similar numbers of insects, and that many amber fixtures in the study were mounted over paved medians with little vegetation, whereas several blue-white fixtures stood beside shrub beds. Ruiz concludes that the study does not clearly isolate the effect of light color.
Based on Ruiz’s comments, it can reasonably be inferred that ____
Which choice most logically completes the text?
For SAT inference questions like this, first identify whose viewpoint the question is about (here, Ruiz) and quickly restate that person’s main point in your own words. Then underline the specific evidence they cite and ask what that evidence suggests indirectly (for example, that another factor might be influencing the results). Finally, eliminate choices that are too extreme (using words like "always," "every," or "immediately"), that contradict the speaker’s tone (cautious vs. confident), or that introduce ideas not supported by the passage, and select the option that most closely matches the implied reasoning without going beyond it.
Hints
Focus on Ruiz, not the city official
The question asks what can be inferred from Ruiz’s comments, not from the city’s conclusion. Reread the sentences that mention what Ruiz notices and concludes.
Notice the other variables Ruiz mentions
Ask yourself: besides light color, what other differences between the two sets of lights does Ruiz point out (for example, the presence of the moon or vegetation)?
Connect Ruiz’s evidence to his conclusion
Ruiz says the study "does not clearly isolate the effect of light color." What does it mean for a study to not isolate an effect, and how do moonless nights and vegetation relate to that idea?
Eliminate absolute or overconfident statements
Check whether any answer choices make universal claims (like "always" or "every") or say the evidence is fully definitive. Do those match Ruiz’s more cautious, critical tone?
Step-by-step Explanation
Restate what the city claims
The city official claims that, because observers usually saw fewer insects around amber LEDs, amber lights must attract fewer insects and should replace blue-white lights. This treats light color as the main cause of the difference in insect counts.
Understand Ruiz’s objections
Ruiz gives two specific concerns:
- On moonless nights, both light types had similar insect numbers, weakening the idea that color alone always makes a big difference.
- Many amber lights were over paved medians with little vegetation, while several blue-white lights were by shrub beds (more plants).
These points suggest other factors besides color could be affecting how many insects show up.
Infer what Ruiz is implying
If moonlight and vegetation differ between sites, then the study is mixing up (or confounding) several variables at once. Ruiz’s conclusion that the study "does not clearly isolate the effect of light color" means that differences in insect counts might be partly or entirely due to where the lights are (pavement vs. shrubs, etc.), not just their color.
Match that inference to the best answer choice
We need the choice that reflects Ruiz’s idea that the study’s results might be explained by site conditions rather than light color alone, and that therefore the study doesn’t cleanly separate the effect of color. Choice D — "the study may not have isolated the effect of light color because site conditions could have influenced insect counts" — directly captures this reasoning and is therefore the best completion of the text.