A high school has found that, for each of the last 15 years, the average grade point average for members of the cross-country running teams has exceeded the average grade point average for the school as a whole. This phenomenon can most likely be attributed to the fact that long distance runners have so much time to think while running that they can essentially study as they run.
Which of the following most undermines the conclusion drawn above?The conclusion is that cross country runners have higher GPAs because running gives them time to study mentally while they run. To undermine this, we want a different reason the cross country team’s GPA is higher, such as the team attracting students who already have high GPAs. That would break the claimed cause and effect. Selection bias is the key idea.
A. Cross-country running is more strategic than many realize, requiring runners to expend mental energy thinking about race tactics.
This makes the “they can study while running” story less believable, because their mental attention may be used for tactics instead. But it still does not explain why their GPA is higher, so it is a weaker underminer than an option that gives an alternative cause.
B. Many cross-country runners are also members of the track-and-field team, for which the average grade point average is actually lower than that of the school as a whole.
This does not weaken the conclusion. If anything, it would make the cross country team’s high GPA seem even more surprising, since some members belong to a lower-GPA group.
C. The cross-country team is among the few teams that do not require a try-out, making it a popular activity for high-achieving students who want to list a sport on their college applications.
This directly undermines the conclusion by giving an alternative explanation: high-GPA students are more likely to join cross country for college application reasons. Then the team’s higher GPA is not because running lets them study, but because the team is made up of students who already perform well academically.
D. Because the nearest cross-country trails are a long distance from the school, cross-country is one of the most time-consuming activities the school offers.
This tends to go the other way. If it takes more time, that would usually reduce study time, which would make the conclusion less plausible, but it still does not explain the higher GPA as well as the selection-bias explanation in C.
E. The cross country team's average grade point average has dropped each of the last three years.
This is irrelevant to the causal claim. The team can still have a higher GPA than the school overall even if its GPA has been decreasing recently, so this does not undermine the proposed explanation.
Answer: (C)