Q25 - Advertisement: The dental profession knows that

[ohthatpatrick]

Question Type:
Match the Flaw

Stimulus Breakdown:
Conclusion: Dental profession agrees that Blizzard is the best way to fight cavities.
Evidence: We surveyed five dentists, and they all said Blizzard's tartar control is the most effective cavity-fighting available.

Answer Anticipation:
There's a pretty big leap from "we surveyed five dentists" to "the dental profession agrees". It looks like we should be looking for a sampling flaw that over-extrapolates from a small sample size.

Correct Answer:
D

Answer Choice Analysis:
(A) No. This has extrapolating from a small sample, but it also has a drift between what the survey was about (popularity) and what the extrapolation is about (best policies).

(B) No, the conclusion is about "some voters", so this couldn't replicate the same overly bold extrapolation.

(C) No, the sample size sounds too big: "thousands of voters"?

(D) Yes. This has extrapolation and the survey and the conclusion both are dealing with "best way to help the nation". In this case, Gomez's policies is a match for Blizzard's tartar control formula.

(E) No, it's got the sampling flaw but the survey is about one thing (would Gomez help?) and the conclusion is about something else (would Gomez be the BEST option?).

Takeaway/Pattern: With Matching questions, we never know how coarse-grained or how specific our prephrase needs to be. If we were just looking for a Sampling Flaw, we could remove (B) and (C). But in order to get the closest match, we wanted ONLY a Sampling Flaw, not the additional topic-shift flaw in (A) and (E).

#officialexplanation

[gplaya123]

A vs D please

[csunnerberg13]

A vs D please

So the stimulus says that
Because 5 surveyed dentists all agreed that a part of the Blizzard formula is the most effective formula available,
dental professionals know brushing with Blizzard is the best way to fight cavities.

So for flaws, we want something that has that a small group is supposed to represent a whole profession and something with a language shift (like from the most effective available to the best way).

There are some other elements that are important to look for too, like concept that it's claimed the dental profession KNOWS, and the use of comparative language in the conclusion.

(A) is probably the best of the wrong answer choices. It has that the nation's voters know something due to the agreement of ten people who said he is "very popular". I rule it out because of "very popular" - we want a conclusion that says it's better than the others available...very popular doesn't tell us anything comparatively. I had this answer choice left when I was down to 2, but ultimately D is better because it has that comparative aspect.

(B) You can eliminate right from "some of the nation's voters believes" - we want something that says the whole group knows, not some of the group believes.

(C) Totally wrong - "generally believe" is a mismatch; "polled thousands of voters" is unclear whether the poll was representative, but we want something that is very obviously non-representative, like 5 voters. It does at least have the comparative conclusion, but for the other reasons it's still a mismatch.

(D) correct answer. We have the nation's voters knowing something based on the opinion of an under-representative group, and a conclusion about being better than the other options.

(E) says "we know"... well who is "we"? what group are we referring to? Did a large group know based on the opinion of a small group? well we're not sure, because we don't know how big "We" is.

hope this helped

[asafezrati]

Here's a more complete picture of the flaws I've seen:

1. The premises are about toothpastes only, but the conclusion is broader - "bext way to fight cavity." Pulling your teeth out might be much better than toothpastes.
2. The small sample.
3. The formula in the toothpaste is the best among formulas, but who says that any other toothpaste doesn't use this formula?
4. The formula is only one ingredient. Maybe even though the formula is supar awesome, the toothpaste includes sugar as a main component. Not very helpful for preventing cavities.

D fits in all of these.

Two questions about C:

1. I think that "generally believe" fits "know". Are they indeed the same in these arguments?
2. I've got a problem with the numbers. We don't know the total number of the population, so theoretically the five dentists can be more or less representative than the thousands of voters. I think that in both cases we just don't know if the sample is representative. Is there a mismatch in the flaw here?

Thanks.

[ohthatpatrick]

Nice thoughts!

Naturally, "know" vs. "believe" has SOME distinction, in a vacuum, but in this context they seem like pretty equivalent expressions.

An advertisement saying "The dental profession KNOWS ______" sounds like it's just generalizing about what dentists would generally believe.

Of course, while I could live with "generally believe" in (C), I can certainly agree that "The nation's voters KNOW" in (D) is a stronger match.

I don't really think you can make a case that the sample size in (C) is too small, regardless of the ultimate population.

A few thousand people is a robust sample size. As long as its a representative sample of people, we would extrapolate its results to ANY population size.

Meanwhile, TEN voters or FIVE dentists is a glaringly small sample size.

A sample's size and representativeness are two different things, even though the former can sometimes help us to better achieve the latter.

I'm not a statistician, so I don't know official cut-offs, but I think the respected sample size for a poll / survey is AT LEAST in the hundreds and usually around 1000 or so. The representativeness, I assume, relates to the meaningful demographic categories within the population being surveyed.

So if there are five different specialties or schools of thoughts in dentistry, it's possible that this sample is representative but not large enough. And it's possible that (C)'s sample is large enough but not representative.

But, to clarify, (C)'s sample IS large enough.

Meanwhile, the sample size in the original stimulus and in (D) is definitely too small.