Logical Reasoning

PT144 · S4 · Q13 Government statistics show that

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Government statistics show that the real (adjusted for inflation) average income for families has risen over the last five years.

Conclusion (therefore)

The Anderson's real income (adjusted for inflation) must have increased over the last five years.

Evidence (since)

Government stats show that real average income for families has risen over the last five years.

The Andersen family's income is average for families.

Evaluate

This seems to be some sort of mathematical flaw, playing off two different usages of the word "average". Let's flip into objection mode:

Given that ... the Anderson's have a family income that is average for families (like if the average family income is $100k, their family income is $100k),

and given that ... average income for families has risen over the last five years.

How could we still argue that .... the Anderson's income has not increased over the last five years?

Well, naturally when we hear , that does not mean that all families' income has risen. Some have gone up. Some have stayed the same. Some have gone down. But overall, once you average all those stories together, the average has moved up.

So we can seemingly just say that the Anderson's weren't lucky enough to be beneficiaries of this recent trend of rising family income. Maybe they also had a family income of $100k five years ago. Maybe they even used to make $180k, and then Mr. Anderson got laid off, and now they're only making $100k.

Goal

The fact that the Anderson's currently have the average family income doesn't mean that their family income has behaved as "average family income" has over the past five years.

13.

The reasoning in the argument is most vulnerable to criticism on the grounds that the argument

ambiguously uses the term "average"
Not Equivocation
This answer alludes to the famous Equivocation flaw, in which the same term is used two different times to mean two very different things. (This answer is almost always wrong). The two usages of 'average' in this argument are comparable. They're both talking about the "average income for a family". The first instance is saying, for the past five years that number has risen. The second instance is saying, the Anderson family's income currently matches that number.
20% picked this
fails to take into account
Contradicted
It does not fail to take into account inflation. It says that the Andersen family's real income must have increased, and "real income" is adjusted for inflation.
5% picked this
overlooks the possibility that most
Not an Objection
Since this begins with fails to consider / overlooks the possibility, we can ask ourselves whether the idea that follows weakens. Can we object to the argument by saying, "Hey, author -- most families' incomes are below average"? No. We are explicitly told that the Anderson family's income is not below average; it is average. We're not trying to argue that their income isn't average. We're trying to object by arguing that their income hasn't increased over the last five years.
3% picked this
Correct
fails to consider the possibility
Why this is right
Since this begins with fails to consider / overlooks the possibility, we can ask ourselves whether the idea that follows weakens. Can we object to the argument by saying, "Hey, author -- the Andersen family's real income was above average in the recent past"? Sure! If their income was recently above average, and now it's just average, then it sounds like the family's real income has recently declined. That goes strongly against the conclusion that "their income must have increased over the last five years".
Skill tested: Flaw · how this choice captures the argument's function is the move to repeat next time.
71% picked this
presumes, without providing justification, that
Not Assumed / Too Strong: no errors
Since this begins with presumes / takes for granted, we can ask ourselves whether the idea that follows was something the argument needed to assume. The argument definitely wasn't assuming that the government is 100% perfect in gathering accurate estimates of family income. Even if they are only 99% accurate, this argument would make just as much sense.
1% picked this

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