Q15 - A consumer magazine surveyed

[dan]

15. (C)
Question Type: Weaken the Conclusion
This argument has many issues and many assumptions. For one, the argument is based on data that may contain sample bias. A higher percentage of the "more than 6 months" group reports being satisfied with the treatment. But these are people who have opted to continue treatments! Isn’t it likely that the "more than 6 months" group is a self-selecting group of people who tend to like the treatments, and so elect to continue with the treatments? Here’s an analogous case:

60% of those who have seen the Star Wars trilogy exactly one time report having liked the trilogy. 95% of those who have seen the trilogy two times or more report having liked the trilogy. Thus, the more one sees the trilogy, the more one likes the trilogy.

No! Not necessarily. Maybe the people who already liked it the first time opted to see it multiple times. This would obviously skew the data. Answer (C) expresses the possibility of a biased sample, which would certainly weaken the argument.

(A) is irrelevant to the argument (we already know that 36% said things got better, so it’s no surprise that some of the others said things got worse).
(B) is very tempting, but keep in mind that the response rate is irrelevant. The argument is based on those who have responded.
(D) actually strengthens the argument by raising the possibility that the number of "more than 6 months" patients who are satisfied is actually underrepresented by the survey.
(E) is irrelevant to the conclusion.


#officialexplanation

[LSAT-Chang]

Hello MLSAT instructors!
I had a question about answer choice (b)...

At first I thought: well, if patients who had received treatment for longer than 6 months are more likely to respond, then maybe there are so many more people in that group who responded than the other group (less than 6 months of treatment), so it is more likely that they will get positive responses than the other group, so that would skew the results. But then I thought, "well.. maybe not really, since it could also have been the case that there were more people repsonding negatively to it, so I can't really assume that having patients in a certain group be more likely to respond to a survey would necessarily mean that they would respond positively". Is this why (b) would be wrong??

and (c) would be correct since if patients who feel they are doing well tend to remain in the treatment, then it is very likely that there will be more positive responses from that group of people, right? So if: 5 people in the less than 6 months treatment group responded, whereas 100 people in the longer than 6 months responded (giving 20% in the first, and 36% in the last) then there would be only 1 person responding positively to the treatment in the first group whereas there would be 36 people who responded positively - so if we say that "patients who feel they are doing well in treatment tend to remain in treatment, while those who are doing poorly tend to quit earlier" - we can't really conclude that psychological treatment lasting more than 6 months is necessarily more EFFECTIVE than shorter-term treatment since those group consists mainly of people who feel they are doing well - right? I feel like I'm lost all of a sudden after giving this whole explanation..

Can anyone clear this up for me??

[bbirdwell]

Doesn't seem like any clearing up is necessary. That all sounds good to me!

[gplaya123]

Hey Matt,
so would you say that
C points out the Sampling fallacy whereas B points out the #vs% fallacy?

Also since argument doesn't talk about number of respondents, rather talks about whether the treatment is effective or not, C is the answer?

[fimtiaz7]

Hi Instructors,
I've read the explanation and the explanation of star wars trilogy. But, i am not convinced. the way i am reading this argument is that the conclusion i.e. psychological treatment lasting more than 6months is more effective than shorter-term" is based on the premise that the response rate for shorter term treatment is 20% i.e lower compared to long-term 36%. Now, if i consider another analogy of a medication A i.e. antibiotic. I can say that it is effective in short term i.e. 2 pills. But, it is more effective if someone takes 5 pills. now, like the star war analogy, of course taking 2 pills is effective in the first place but taking 5 pills i.e. increasing the rate or frequency increases its effectiveness..hence, i don't get it why C is a weakener? I rather see B as the candidate that destroys the argument.

Can someone please help!
Thanks,
Farheen

[renata.gomez]

I would also appreciate another explanation.

Thank you!

[LolaC289]

(B) is very tempting, but keep in mind that the response rate is irrelevant. The argument is based on those [i]who have responded

Actually I think the response rate is not irrelevant in here.

But (C) is a better answer than (B) because (B) has the potential to either weaken or strengthen. If (C) doesn't exist, I will go with (B).

Survey Result:
Among the people who received treatment for 1 month, 20% of those who responded to the survey claimed effective.
Among the people who received treatment for 7 month, 36% of those who responded to the survey claimed effective.

Conclusion:
7-month treatment is more effective than 1-month treatment.

(B) said maybe people in the 7-month group are more likely to respond to the survey. This could possibly weaken or strengthen, depending on whether those who more likely to respond are positive or negative. For example,

1m group and 7m group both have 100 patients.

Among 1m group, only 20 people responded, so among them 2 claimed positive.

Among the 7m group, 50 responded, among them, 18 claimed effective, 32 claimed not effective. 50 didn't respond.

(B) affects the results by implying the attitude of those who didn't respond.

IF in 7m group, it's those who already think the treatment is effective are more likely to respond, then this weakens the argument.

Because it tells us that in that group, those 18 people are more likely than others to respond positively. So among the 50 people who didn't respond, maybe none think it is effective. Then IF the whole group has responded to the survey, the positive rate is only 18%, which is even lower than the 1m group.

IF in 7m group, it's those who already think the treatment is not effective are more likely to respond, then this strengthens the argument.

Because it tells us that in that group, those 32 people are more likely than others to respond negatively. So among the 50 people who didn't respond, maybe all of them think it is effective. Then IF the whole group has responded to the survey, the positive rate is 68%, which is even higher than the previous 36%.

So (B) can actually go either direction.

(C) however, is an one-way street.