Q15 - Commentator: The reported epidemic of childhood obesit

[ohthatpatrick]

Question Type:
Match the Flaw

Stimulus Breakdown:
Conclusion: The proportion of kids who are obese can't have gone up a bunch.
Evidence: Over the last 8 years, there was only a 1 pound increase in average weight.

Answer Anticipation:
It's hard for me to immediately call out exactly what the flaw is, but I would focus on the idea that we moved from "since average only went up slightly, proportion must've only gone up slightly". The flaw is definitely about the distinction between an average and a proportion. If you wanted the average to stay around the same, but you wanted to have a higher proportion of obese kids, you'd just have to balance them out with a higher proportion of skinny kids. In other words, maybe 8 years ago, all the kids were 120 lbs (not obese). If nowadays there are lots of kids who are 80, many who are still 120, and a bunch that are 160 (obese), then the average would still be around 120, but proportion of kids who are obese went up (from none to more than none). I'd look for some argument that matches "If the overall average is essentially the same, then a subset didn't go up much."

Correct Answer:
B

Answer Choice Analysis:
(A) I wouldn't get past the first half of this one. The PREMISE is supposed to be "the average is basically the same". In this one, the CONCLUSION is saying "the average must have gone up".

(B) YES, this works. PREM: average is basically the same. CONC: this subset must not have gone up.

(C) Nope. The CONC is saying "a subset must have gone up". A matching conclusion would be saying that a subset had NOT gone up.

(D) Nope. The CONC is saying "the average must have gone up".

(E) Nope. The CONC is saying "the average must have gone up".

Takeaway/Pattern: Wow, they really made this easy, as long as we identified the argument core: "since average barely increased, the proportion of X must not have increased much." Three of the answers, (A)/(D)/(E), concluded "the average did increase", which is a mismatch on two levels. (C) is the only other answer concluding something about proportion, and it says the proportion DID increase substantially, whereas the original and (B) say the proportion DID NOT increase substantially.

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