LR Question 19 Explanation
QUESTION TEXT: A recent study showed that the immune system blood…
QUESTION TYPE: Necessary Assumption
CONCLUSION: Tea boosted the immune systems of participants in the study.
REASONING: Compared to people who drank coffee, the immune systems of tea drinkers responded twice as fast.
ANALYSIS: This is a bad study: there’s no control group. The conclusion compares tea drinkers to regular people, but the evidence only compares tree drinkers to coffee drinkers.
It’s possible that coffee hurts immune systems. In which case tea may not actually help: it would only look good compared to coffee.
___________
- This doesn’t matter. The argument was only comparing those who drank one liquid but not both.
Negation: One person drank both coffee and tea. They weren’t considered in the argument. - It doesn’t matter if coffee has other health benefits. The argument is only talking about coffee and tea’s effects on the immune system.
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CORRECT. If coffee caused response time to double, then that means that tea had no impact. E.g.
- Regular response time: 5s
- Tea response time: 5s
- Coffee response time: 10s
Negation: Coffee caused immune system response time to double.
- The author didn’t say the study was about regular coffee and tea drinkers. Researchers could have given random people coffee and tea.
Also, even if the study was about regular drinkers, the negation of this answer makes coffee drinkers healthier, so we would expect faster immune response. The fact that that didn’t happen strengthens the argument.
Negation: Regular coffee drinkers have healthier habits than tea drinkers do. - It doesn’t matter if coffee and tea have some stuff in common, as long as they’re not identical.
Negation: Coffee and tea have one chemical in common, and 1,000 chemicals that are different.
I still cannot understand the math behind a “C” answer. If coffee causes the blood cell response time to double, then tea still take half as long to respond to germs. How is it that you say in this case tea has no impact?
The stimulus tells us that the immune system blood cells of tea drinkers took half as long to respond to germs as did those of coffee drinkers–not half as long as those of the general population. And yet, the conclusion says that tea has an immune-boosting effect, regardless of whether someone drinks coffee or not. There’s no control group of people who drink neither coffee nor tea. So, what if coffee has a harmful effect on the response time of the general population and tea has no effect? Then, tea drinkers and people who drink neither coffee nor tea would have the same response time (if all other factors are controlled of course), and coffee drinkers would have a higher response time than those groups. For the argument in the stimulus to follow, it would need to assume that coffee doubling the response time isn’t a possibility, because then maybe tea has no effect.
(C) rules out the possibility that coffee is responsible for the doubling effect. So that would help us say with more confidence that tea actually is beneficial.
Hey Lucas, the conclusion uses “participants’ immune system”, that doesn’t imply the general population, or does it? Also, in (A) if some people consumed both, wouldn’t that dilute the validity of the study. Then when it says tea had some bolstering effect, it could have been the coffee secretly doing it?
That’s correct, the passage is only referring to participants in the study. Though, it would be reasonable to suspect that these results would also apply to the general population who drank coffee, etc.
The problem with A is you could negate it to “one person drank both”. If the study had 1,000 people, then this difference wouldn’t matter. Zero and one are basically the same in this case.
A good necessary assumption answer will have a meaningful negation.
Note: This is an old comment but I wanted to clarify the point.
Is there another leap from “blood cells respond to germs” to the conclusion of “boosted the participant’s immune system defense”? I feel these to concept might need an assumption to bridge the gap.
No leap. If you read the first sentence of the stimulus, it’s pretty clear they’re talking about the response of immune system blood cells.