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Among people in Tiravia who had a fatal car accident while driving, 5 percent of those under 50 years old were found to have prosinopsis, a currently untreatable eye disease that causes a gradual deterioration in peripheral vision. Yet, according to medical records, only 3 percent of Tiravians under 50 have been diagnosed with prosinopsis. Therefore, when a Tiravian driver under 50 has prosinopsis, the disease significantly increases the likelihood that the driver will have a fatal car accident.
Which of the following, if true, most seriously weakens the argument?
| Text from Passage | Analysis |
| Among people in Tiravia who had a fatal car accident while driving, 5 percent of those under 50 years old were found to have prosinopsis, a currently untreatable eye disease that causes a gradual deterioration in peripheral vision. |
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| Yet, according to medical records, only 3 percent of Tiravians under 50 have been diagnosed with prosinopsis. |
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| Therefore, when a Tiravian driver under 50 has prosinopsis, the disease significantly increases the likelihood that the driver will have a fatal car accident. |
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We start with a statistic about fatal accident victims (5% had prosinopsis), then get a comparison point from the general population (3% have prosinopsis). The author uses this higher rate among accident victims to conclude that the disease causes increased accident risk.
Having prosinopsis significantly increases the chances that a driver under 50 will have a fatal car accident.
This is a statistical correlation argument. The author compares the rate of prosinopsis in accident victims (5%) to the rate in the general population (3%) and concludes that the higher rate proves the disease causes more accidents. The logic assumes that correlation equals causation.
Weaken - We need to find information that reduces our belief in the conclusion that prosinopsis significantly increases the likelihood of fatal car accidents for drivers under 50.
The argument makes quantitative claims (5% vs 3%) and a causal claim (prosinopsis significantly increases accident likelihood). The key comparison is between the rate of prosinopsis in accident victims versus the general population.
To weaken this argument, we need to find alternative explanations for why prosinopsis appears more frequently in accident victims (5%) than in the general population (3%). We should look for scenarios that show this 5% vs 3% difference doesn't actually prove that prosinopsis causes more accidents. We can attack the representativeness of the data, alternative explanations for the statistical difference, or issues with how the disease is detected or diagnosed.
This choice says people with advanced prosinopsis can't drive due to severe vision problems. While this might seem relevant, it actually doesn't weaken the argument. The argument is about drivers who do have fatal accidents while driving, so this choice doesn't explain why we see a higher rate of prosinopsis in accident victims versus the general population. If anything, this might strengthen the argument by suggesting that even moderate stages of the disease could be dangerous.
This states there are reliable tests for early-stage diagnosis of prosinopsis. This information doesn't weaken the argument at all. The existence of reliable tests doesn't change the statistical comparison between accident victims (5%) and the diagnosed population (3%). In fact, if reliable tests exist and are being used, it might make the 3% figure more trustworthy, which would actually support rather than weaken the argument.
This explains that early-stage prosinopsis can only be detected through lab tests that few people under 50 actually get. This is the correct answer because it directly undermines the reliability of the 3% baseline figure. If most people under 50 don't get the necessary lab tests, then the true rate of prosinopsis in the general population could be much higher than the reported 3% - potentially even higher than the 5% found in accident victims. This eliminates the statistical foundation the argument depends on.
This provides demographic information about who gets diagnosed with prosinopsis, noting that while most diagnosed patients are over 50, many are in their 30s and 40s. This information is irrelevant to the argument, which focuses specifically on the comparison of rates between accident victims and the general population under 50. The age distribution of diagnosed patients doesn't affect the 5% versus 3% comparison that drives the conclusion.
This clarifies that prosinopsis only affects peripheral vision, not other aspects of vision. Like choice B, this doesn't weaken the argument. The argument already established that prosinopsis affects peripheral vision, so confirming this is the only vision effect doesn't change the statistical reasoning or provide an alternative explanation for why the disease appears more frequently in accident victims.