#23 - Research indicates that 90 percent of extreme

[JKing]

Some of these I got right and I just need to make sure I am on the right path to getting them right. I hope this is not too much, if it is I can next time make these questions in different posts.

December Test 1998

LR Section 1

#23- I picked C but am still uncertain why it is correct

[Steve Stein]

Hi JKing,

Some of the numbers and percentages questions can be tricky. In that one, we know that 90% of insomniacs drink coffee. But all we know about Tom is that he drinks coffee. Without knowing the portion of coffee drinkers who also have insomnia, there is no way to tell how likely it is that Tom is an insomniac.

Consider this hypothetical:

What if there are one million coffee drinkers in the world, but only ten insomniacs. Sure, most of those insomniacs--9 out of the 10--drink coffee, but that is quite a small portion of the million and nine coffee drinkers in the world.

I hope that's helpful! On another note, how have you been preparing for the test? Read any books? taken a course? done some PrepTests?

Let me know--thanks!

~Steve

[est15]

I prephrased the flaw as: the argument draws a cause and effect conclusion from two sets that show correlation (extreme insomniacs and coffee drinkers), which is why I chose (E). I thought (E) captured the cause and effect flaw nicely. What makes that answer choice incorrect?

[KelseyWoods]

Hi est15!

Careful with this one....the author doesn't draw a causal conclusion. He states that since Tom drinks a lot of coffee, it is quite likely that he is an insomniac. But he never says that drinking coffee causes insomnia.

The flaw here is that research tells us that most extreme insomniacs consume large amounts of coffee. From that, we could conclude that if you are an insomniac, you likely consume large amounts of coffee. But we don't know that Tom is an insomniac. We only know that he drinks a lot of coffee. And we don't know what percentage of heavy coffee drinkers are extreme insomniacs.

The flaw is almost a Mistaken Reversal, but since our relationships are not absolute, this of course isn't a conditional reasoning error.

Answer choice (C) gets at the flaw by telling us that we don't know the percentage of heavy coffee drinkers who have extreme insomnia, which means we can't make any conclusion as to whether or not Tom suffers from extreme insomnia based on his coffee drinking.

Hope this helps!

Best,
Kelsey

[reop6780]

I thought this was 'mistaken reversal.' Hence, Kelsey's response helped me directly why I could not find an answer that I expected.

So, whenever I see the original condition with most or some that are not absolute, I should not expect an answer that points out 'mistaken reversal' ..?

Also, I am still confused of what answer C does; percentage of extreme insomnia among ppl who drink large amounts of coffee.

For example, if I new the info of such percentage, can the conclusion, Tom is an extreme insomniac, be properly inferred?

[Sherry001]

Hello hello!
I had a bit of trouble with this problem,because it is numbers and percentages and so I automatically freak out - here's my reasoning could you please see if I am thinking correctly with percentage questions?
And if you could help me get rid of D it'd be awesome .

1- research indicates that 90 percent of extreme insomniac as consume large amounts of coffee.
2- Tom drinks a lot of coffee.

C: it's quite likely that he is an extreme insomniac .

My thinking before I jump to the choices ! ( I remember my instructors voice telling me "percentages don't tell us the whole story, give me more info ") so in this case for us to establish Tom is insomniac .. We need to know how many coffee drinkers thiere are in total and perhaps the number of insomics that drink coffee.?

Also would the authors argument be correct if he had stated ALL insomniacs drink coffee?


A)tempting but no. Because the author says likely .
B)nope author never said anything causal
C) yep.
D) don't know why this is wrong. Is it because it's not a flaw to draw a conclusion about a person that falls under some characteristics ?
E)never does this.

Thanks so much
Sherry

[Lucas Moreau]

Hello, Sherry,

You've got it!

Your spotting of the percentage was well done. We know that 90% of extreme insomniacs drink coffee, but we have no idea whatsoever how many coffee drinkers are extreme insomniacs.

Sometimes for Numbers and Percentages questions, I like to come up with fake numbers that demonstrate the conclusion I'm going for. For example, let's say that there are 100,000 people total who could be described as "extreme insomniacs". So 90,000 of those are heavy coffee drinkers. But if 100,000,000 people total drink coffee (and the real number is much higher than that ), then knowing that somebody is a coffee drinker doesn't tell you at all whether or not they're an extreme insomniac, just 90,000 out of 100,000,000.

Your other logic is sound. D is wrong because it's talking about a logical error of a type of argumentation that isn't present here. Sometimes people have attributes as a class that they don't possess individually, or at least not uniformly distributed. This error in logic would sound more like "Because Jake is from Wellington, and Wellington is a rich town, Jake must be rich".

Hope that helps,
Lucas Moreau

[PeterC123]

Hi,

I thought the argument said this: b/c a group (most insomniacs) have this trait (lots of coffee), and b/c one person (Tom) also have this trait, he is part of the group. Isn't this what D describes?

And piggy backing on one of the questions from before that was not answered, so you are saying even though the argument went backwards, ie from coffee to insomniacs, this does not count as mistaken reversal because its a formal logic with most instead of absoluteness?

Thanks,

[Kristina Moen]

Hi Peter,

Yes, conditional reasoning establishes a relationship between two conditions, where one condition is necessary for the other condition to occur. Here, the statement that "90% of extreme insomniacs consume large amounts of coffee" does not establish a conditional relationship. Apparently, drinking lots of coffee is not necessary for insomniacs because 10% of insomniacs do not consume large amounts of coffee. And likewise, if I know that someone is an insomniac, I cannot infer that they drink coffee. Thus, no conditional relationship has been established.

To speak to your first question - We are told what 90% of insomniacs do. However, the premise says that Peter also does what 90% of insomniacs do. The premise does NOT say that he is part of the group of insomniacs. That's the conclusion that the author is trying to get us to believe!

Answer Choice (C) describes the flaw. We are told that most insomniacs drink coffee. We are told Peter drinks coffee. We are not told what most coffee drinkers do. Thus, we cannot get the conclusion that Peter is most likely insomniac.

If it helps, here's a real-life example: "90% people of people studying for the LSAT have a computer. John has a computer. So it is likely that is studying for the LSAT." The flaw here is that we are not told about the percentage of computer owners who are studying for the LSAT. For example, we might be told ".02% of people who have a computer are studying for the LSAT." That would sure throw off our conclusion!

[PeterC123]

Awesome, got it thanks!