#13 - Government statistics show that the real

[mokkyukkyu]

Hello,

I think I did not understand the "this year the Andersen family's income is average for families"...what does this mean?
I chose A thinking they are using the average in 2 different meanings....

[Nikki Siclunov]

Hi mokkyukkyu,

At issue is the following claim:

...this year the Andersen family’s income is average for families...

The statement can only mean one thing: this year, Andersen family's income was equal to the average family income. If the average family income is $50,000 this year, that's also how much the Andersens are making today.

The error in reasoning has nothing to do with how the average income is defined: both the premise and the conclusion use real (adjusted for inflation) average income. The issue is quite different. From the premises, we know that the average family income has gone up. But, was Andersen family's income "average" five years ago? If not, then we cannot conclude that their income also went up. Consider the following hypothetical: What if the Andersens had above-average income 5 years ago, and above-average incomes did not increase at all? The fact that the Andersens are "average" today could be explained by the fact that everyone else's income caught up with theirs.

Do you see the issue? We just have no evidence that the Andersens belonged to the group of people whose incomes purportedly increased. Answer choice (D) highlights this issue, and is therefore correct.

Hope this helps!

Thanks,

[avengingangel]

Is this a "whole-to-part" flaw ?

[Adam Tyson]

That's certainly one way to look at it, angel! Just because a certain group (families) has undergone a change as a whole does not mean that a single member of that group (one family) has undergone that same change.

We also look at this one as being a "numbers and percentages" flaw, because a change in an average is potentially made up of lots of individual changes. Some families may have seen an increase while others saw a decrease and still others stayed the same. The average going up does not prove anything about any particular member of the set, and being a member of the set that is exactly at the new, higher average tells you nothing about where that member of the set was when the average was lower. That member could have stayed the same (and thus have been above the average previously), could have dropped (and been even farther above the average previously), or could have increased (and been at or below the average previously).

You can also view it as a "time shift" flaw. Just because they are "average" now doesn't prove that they were "average" in the past! They could have been average, but they could also have been above it or below it. Usually we see time shifts based on using the past to prove the present or future, but here it's just as wrong to try to use the present to prove something about the past.

This is one reason why we don't stress "labeling" flaws as a goal in analyzing these questions. Your label for this flaw is no more or less correct than my two alternative labels! There are many ways to view various stimuli, whether from the perspective of what to call a flaw, or how to diagram a conditional relationship, or how to set up a logic game, or how to describe a particular method of reasoning, and so on. There are many tools that will help you get the job done! How you use those tools is up to you!

Nice work, keep that up!

[avengingangel]

That all makes sense. Thanks, Adam!

[Tarte au chocolate]

why isn't A right ? when do we know a term is used in ambiguous terms or not?

[Adam Tyson]

An answer like A, about the vague or uncertain or shifting use of a term, is correct only when you can clearly see two different definitions of a term or phrase being used by the author, Tarte au chocolate. Here, average just means the total amount of something divided by the number of things in the set. The use of the term is consistent throughout the stimulus, and so this answer does not describe the flaw. To see that flaw in action with the word average, we would need something like this"

"My Uncle is an extraordinary person of exceptional character who excels at everything he does. He is above average in every way. So he cannot possibly have an average income."

Here, "average" is being used to mean "ordinary" to describe my Uncle, but then used in the mathematical sense to discuss his income. In this case, answer A would be a good choice.

[AnimalCrossingLSATer]

Hi PowerScore -

So I actually got D (the correct answer) on this one, but on an untimed do-over, I ended up switching to B. I’m posting this on here (at least at the time of submitting this post) since none of the above responses on this thread address incorrect answer B in particular and would like clarification on why B is incorrect.

What led me to B on my untimed do-over is that, in the stimulus, the Andersens’ income this year is average for families. It doesn’t say “real income” explicitly, defined as adjusted for inflation per the first sentence, and thought, “ok, well, the stimulus seems to equate “Andersens’ family income is average for families” with “Andersens’ real family income”.

If I’m interpreting B correctly, then it would seem like B, when added, would result in something like:

“...this year the Andersens’ real family income is average → their income must have increased over the last five years”. On the premise that the real average income for families, according to government statistics, has risen over the past five years.

After reading that, I feel like this would commit a whole-to-part flaw (as alluded to in another earlier post on this thread), because the premise is on the average of families, and then taking that quality (lower after five years) applicable to the whole (“families'') and applying to the Andersens’, only one member of the whole. Thus, B seems to still leave the argument to be flawed, even after accounting for inflation with respect to the Andersens’ income.

So, my question is: is that (the above explanation) why B is incorrect?

For what it’s worth: here was my line of thinking into D during my timed section on the first attempt, if this makes a difference (either to whoever takes this question or anyone reading this explanation in the future, and if this is correct):

(Paraphrased): “...the Andersen family’s real income must have gone up over the previous five years”.

My thoughts: “Must?! Huh?! What do you mean “the Andersens’ income MUST have gone up?! What?!”

Anyway, after taking a breath to chill out after seeing that…

This is a Flaw in the Reasoning question, and I admittedly didn’t come up with a pre-phrase leading to the answer choices, but my mindset was: the answer choice would make it more likely that the Andersens’ real income didn’t necessarily increase over the last five years (in other words, attacking the conclusion by accounting for the logical opposite of the stated conclusion). The stimulus only states that the real average income for families went up over five years. But if the Andersens’ real income was ABOVE average...well, nothing in the stimulus states what must happen if one’s family’s real income is above-average, right?

Since it seems like there is no certainty over what MUST happen in the above average-group, and that, as one of the earlier posts addressed, it’s not clear whether the Andersens would still be part of that “average” group, then it leaves open that possibility that the Andersens’ income may not have increased over the last five years. That’s why I chose D, at least in my timed attempt.

Thanks very much for your assistance with this!

-Dustine B. (“AnimalCrossingLSATer”)

P.S. My last few posts on the forum have been awfully long (and with a few grammatical typos), so thank you so much for taking the time to read these! I find that asking questions with a detailed explanation of my thought process would potentially give me the most benefit as a user of this forum. Happy to condense my posts in the future.

[Robert Carroll]

Dustine,

There is no need to adjust for inflation this year, which is the only place the stimulus doesn't provide the modifier "real" on "family income". Adjustment for inflation has to happen with previous years because a dollar in 1998 might not be a dollar in 2003. But if we're in 2003 talking about 2003 income, the family's income IS their real income, because adjusting for inflation would put their income into present terms. In the present, it's already in present terms. So answer choice (B) isn't a flaw here - as you point out, "fixing" the problem it apparently identifies wouldn't fix anything with the flawed argument in the stimulus.

I think your explanation of answer choice (D) makes the mistake of thinking that there is an average "group" at all. The average is just a statistical abstraction from all the family incomes. No family actually has to make the average, so no family has to be in an "average group" that's uniquely affected by a change in the average. If the Andersens had an income equal to the average now, but greater than the average before, then the premises could be true without the conclusion being true. Largely, I think you got that point, so good job!

Don't worry, we're here to answer your questions! We appreciate the thoroughness.

Robert Carroll