#19 - A recent study showed that the immune system blood

[cecilia]

Hi Powerscore folks - just wanna get confirmation on this question from the June '15 exam. This was a causal argument, no?? I have become accustomed to seeing those types of arguments on strengthen/weaken questions, that I was completely caught off guard on this one since it was a necessary q. and it involved the dreaded "study" - which for me, always ramps up the anxiety.

Could someone confirm that my thinking was correct on this? At times, it feels like being acquainted with basic scientific method (which I am not) is a pretty necessary skill to navigate thru some of the LR questions that have "studies" in them comparing this and that. Not being a hard science major, I feel pretty handicapped.

Thanks in advance and Happy Thanksgiving.

[Steve Stein]

Hey Cecilia,

That's a good question, and you are right about the existence of a causal argument in that example. That one presents an interesting mix of causal reasoning and numbers and percentages:

Exclusive tea drinkers' blood cells took half as long to respond to germs as exclusive coffee drinkers' blood cells.
In other words, the tea drinkers' blood cells were twice as fast as coffee drinkers' blood cells in responding to germs.

The author concludes that an immune system boost from tea must have given the tea drinkers the advantage, and caused this margin between the response times of the two groups.

• Cause Effect
  
  Immune boosting tea tea drinkers faster than coffee drinkers in germ response time

The correct answer to this Assumption question is answer choice (C); the author must assume that drinking coffee didn't actually slow down the coffee drinkers by half. If we apply the PowerScore's Assumption Negation technique, we logically negate, or take away, any given assumption to see whether that weakens the argument. When we negate this answer choice, we get the following:

• Drinking coffee did cause the coffee drinkers' blood cells' response time to double.

This could also have caused the tea drinkers' advantage with regard to germ response time:

• Cause Effect
  
  Immune slowing coffee tea drinkers faster than coffee drinkers in germ response time

The author must assume that this alternative was not the actual cause of the margin in germ response time.

Good question, and an interesting one—I hope this is helpful! Please let me know whether this is clear—thanks!

[cecilia]

It's clear. Thanks Steve!

[bk1111]

Can someone explain why A is incorrect? The stimulus says that participants either drank only coffee or only tea?

[James Finch]

Hi BK,

Answer choice (A) doesn't work because the stimulus is concerned only with those that drink only tea and those that drink only coffee. Even if there are other groups, like one that didn't drink either and one that drank both, we still have data about the two groups we need to know about. But to make sure, let's apply the Assumption Negation technique:

Not all of the participants in the study drank either tea or coffee, and some drank both



Drinking tea didn't necessarily boost the participants' immune system defenses.

But this doesn't follow, because we still have a tea-only group and a coffee-only group, and the tea-only group had immune response times half as long as the coffee-only group. The other explanation for this discrepancy is dealt with in (C), which defends the conclusion against the possibility that drinking coffee causes immune response times to double.

Hope this helps!

[freddythepup]

Hi, I get why A is not correct, but can you please explain why C is necessary? It says in the stimulus that there's a group that drank tea but no coffee, which had the much faster response rate to germs as did those who drank coffee but no tea. If it's clear we're comparing these two different groups who just drank one of the two beverages, not both, why do we need to assume that those who drank coffee did not cause their blood cell response time to double? I get that when this statement is negated, it weakens the argument, but I still don't see why we need it because it would only apply to the group that DRANK the coffee and no tea, not the other group. Thanks!

[Adam Tyson]

You've actually answered your own question here, Freddy - we know that C is an assumption of the argument because the negation of it wrecks the argument. Not just weakens it - DESTROYS it! Why, because if drinking coffee caused the immune cell response time to double, that means that the tea had no impact at all. The difference between the two groups was entirely due to the negative effect of the coffee rather than any positive effect of the tea.

Remember that this argument is about a comparison between those two groups. There isn't any direct evidence that the tea-only group got faster, just that they were faster as compared to the coffee-only group. The author thinks tea caused the difference, so he must be assuming that coffee was not solely responsible for the difference.

[Agent00729]

Couldn't there be a scenario where both groups start out like this, due to some other third cause factor:

Before drinking:

Coffee drinker group: 5 minutes
Tea drinker group: 10 minutes


after drinking:

Coffee drinker group: 10 minutes (doubled)
Tea drinker group: 5 minutes


How do we know they both started out the same? It seems like this scenario would allow for both C and the conclusion to coexist.

Thanks for the help!

[Adam Tyson]

We don't know that, Agent00729, and if there was an answer choice that said there was no crucial difference about the two groups prior to their drinking tea or coffee then we would be looking at an answer that eliminates an alternate cause, and that would also be an important assumption. But none of the answers does that.

Answer C is a required assumption because if it is not true, the logical force of the argument is destroyed. That doesn't mean that the conclusion is false, but only means that the premises no longer offer valid support for the conclusion. The negation of the correct answer doesn't have to disprove the conclusion, which is what I think you may be focusing on here, as it looks like you are trying to show that the conclusion could be true despite the negation of the credited answer. What the negation needs to do is show that the premises we were given are no longer good enough to get us to the conclusion. We are kicking the legs out from under the argument.