Causation & Correlation
Overview
Some arguments rely on an unwarranted assumption that two events that occur together must have a certain cause-and-effect relationship. In other words, some arguments inappropriately conclude that one event caused another based only on the evidence that the two events occurred at the same time or one after the other.
Example: It is common for recent airplane passengers to report feeling jet lagged up to several days after a transatlantic flight. These jet lag sufferers are also likelier than average to be diagnosed with influenza. Therefore, jet lag causes an increased susceptibility to influenza.
This argument assumes a cause-and-effect relationship based on a correlation. The conclusion that jet lag causes the flu is logically flawed; the evidence only establishes that jet lag and the flu occur together. In fact, these two conditions have separate causes: traveling across time zones causes jet lag, and sitting very close to many people causes the flu.
When an argument of this type appears on Weaken Questions, the correct answer will usually show that presuming correlation means causation is a faulty assumption. The correct answer will likely establish this by doing one of the following: 1) showing that the correlation is simply coincidence, 2) showing that some other condition explains the correlation, or 3) showing that the causal relationship is reversed.
Question 1
In response to long-distance truck drivers' concerns about the health risks associated with long drives in open truck cabins, researchers asked truck drivers to estimate both the percentage of time that they leave the windows of their truck cabins open while driving and how often they suffered from respiratory ailments over the last year. The survey results showed that those who kept their windows open more often experienced more respiratory ailments, leading researchers to conclude that open truck cabins cause respiratory ailments.
Which one of the following, if true, most undermines the researchers' conclusion?
Explanation
Researcher's Conclusions:
Open truck cabins cause respiratory ailments.
- Researchers asked truck drivers to estimate both the percentage of time that the drivers leave the windows open and how often the drivers suffered from respiratory ailments over the previous year.
- According to the survey, those who left their windows open suffered from respiratory ailments more often than other truck drivers did.
The answer will undermine the assumption that the correlation between frequently leaving one's windows open and respiratory ailments in (1) is sufficient evidence to conclude that open windows causes such ailments.
Choice C: This fact states that those truck drivers who keep their windows open more often are also more likely to be smokers. This provides a possible alternative cause to the observed susceptibility to respiratory illness. Because smokers may be more likely to suffer from respiratory illness, the open windows may not be the cause of illness among the drivers surveyed, and the researchers' conclusion is weakened. Choice C is correct.
Choice A: The fact that few drivers were inoculated against respiratory ailments suggests that both groups, those who did and did not leave their truck windows open, were equally susceptible to ailments. This provides reason to accept rather than reject the researchers' conclusion.
Choice B: Irrelevant distinction. The failure on the part of researchers to ask the study's subjects to distinguish "between serious and mild respiratory ailments" does not affect either the evidence or the conclusion, both of which describe the frequency, not the type, of ailments.
Choices D & E: Scope shift. The argument describes frequency of respiratory ailments, so it does not need to consider causes of "work missed due to illness" generally or the increased susceptibility to "skin cancer." Neither choice implies or states a relationship between respiratory ailments and days of work missed—or respiratory ailments and skin cancer, so these statements do not affect the researchers' conclusion.
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