#7 - Pollster: When opinion researchers need a population

[Administrator]

Please post your questions below!

[plshelp]

Hi, could you please help explain why C is right and how to approach this problem. I know its a necessary assumption question. I didn't understand the connection between a lower participation rate and less accuracy if participation was voluntary. I assumed that the author was saying that the reason for less accuracy was that there would be less of a sample size and I took that for granted. I then went through the answer choices without a prephrase. I was attracted to answer choices that spelled out more about the assumption that if it were voluntary less people would participate and I narrowed it down to B and E. B seemed to be saying that no new people would be participating if it were voluntary which would confirm the premise that participation would be lower and E seemed to support the premise that participation would be lower because it would support the fact that participation in the mandatory census always would be greater. Is the issue that because the sample size is always just a proportional representation that I shouldn't have focused on numbers as the reason for the lack of accuracy? Or that I shouldn't have focused on supporting the premise that the participation rate would be lower because that is a premise I should just necessary assume is true because its a premise? Can you help me figure out what a better way to approach this question would have been?

[James Finch]

Hi Pls Help,

It sounds like you took a scattershot approach to the question, which tends to lead to the kind of confusion you described. This is an assumption question, so we always need to see whether there is a logical gap between a new element in the conclusion (ie something not in the premises but found only in the conclusion) and the premises; if there is, it's a Supporter type and our answer choice should fill the gap. If not, we have a Defender type that is much harder to prephrase. In this case, we can see that from the two conditionals given:

The premise: If census participation became voluntary, the participation rate would be much lower, or:

CPV PR Down

and the conclusion: If census participation became voluntary, polls designed to discover the opinions of the national population would have less accurate results, or:

CPV LAROP

The obvious way to tie the two together is by saying that whenever participation rate goes down, the polls are less accurate because the lower participation rate doesn't reflect true demographics as well as the results from a mandatory census. So that's the prephrase I would use to answer this question. Let's look at the answer choices:

(A): Out of scope, as we're not concerned with making a census the only way to get accurate demographic data, but with tying a voluntary census to being less accurate.

(B): Possibly appealing on first read, but in fact deals with irrelevant information. People who don't currently participate in the census still not participating if it's voluntary doesn't serve to make a voluntary census less accurate.

(C): Deals with distinguishing voluntary and mandatory censuses, which is the scope we are looking for. Contender.

(D): Irrelevant, we don't care about people who don't participate in opinion polls.

(E): Doesn't deal with what happens in a voluntary census, so it doesn't help us.

So we're left with only (C) by process of elimination, but we can still show it to be correct. Using the Assumption Negation technique, we can see that:

The group of people who would participate in a voluntary national census would not differ in its demographic characteristics from the group of people who would participate in a mandatory national census



Polls designed to discover the opinions of the national population would not have less accurate results

This works perfectly with the premises in the stimulus, showing it to be the correct answer.

Hope this helps!

[dlehr99]

So we're left with only (C) by process of elimination, but we can still show it to be correct. Using the Assumption Negation technique, we can see that:

The group of people who would participate in a voluntary national census would not differ in its demographic characteristics from the group of people who would participate in a mandatory national census



Polls designed to discover the opinions of the national population would not have less accurate results

This works perfectly with the premises in the stimulus, showing it to be the correct answer.

Hope this helps!

Can you help me understand the application of this negation technique? I would logically agree with the answer choice negation:

The group of people who would participate in a voluntary national census would not differ in its demographic characteristics from the group of people who would participate in a mandatory national census

But in the explanation provided the stimulus was also negated.

Polls designed to discover the opinions of the national population would not have less accurate results

Is this just to show the effect of the answer choice negation on the stimulus, as I don't think the technique calls for negating the stimulus. Either way, I'm hung up on how the newly negated answer choice of --voluntary participants not differing in demographic characteristics -- weakens the argument. My thought process is: Okay it doesn't change. That seems like a neutral effect on the accuracy of the results not that they would be less accurate.

AND now I'm realizing that's exactly the point being made above... jeesh . It weakens it because it doesn't agree with the Pollster's comment that there would be less accurate results.

Posting this anyway so an expert can confirm and because I think this might be helpful to others.

[Paul Marsh]

Hi dlehr99! You are right on the money - the negation of Answer Choice (C) weakens the argument because if the demographics are the same, we would expect the accuracy of the polls to be about the same (and therefore the Pollster's conclusion wouldn't make any sense). Nice job working through that! The Assumption Negation technique is a very helpful tool but it can be a bit confusing at first - give it plenty of practice and you'll be able to apply it without tripping yourself up.

As for your first question - when James wrote,

Polls designed to discover the opinions of the national population would not have less accurate results

That was just his way of showing the effect of negating the answer choice! Remember that when we use the Assumption Negation technique, all we do is negate the answer choice in question and then plug it in to the argument. If it makes the argument fall apart, it's the right answer! James was demonstrating that when we plug the negation of Answer Choice (C) into the argument, the conclusion no longer really makes sense and the conclusion becomes false.

Hope that helps!

[dlehr99]

Thanks a lot, and I appreciate you confirming!

[silver2731]

I think I am totally confused.

I agree with the above explanation that we need an assumption that connects the two premises so the logic ends up being: If participation rate goes down, we have less accurate result.

C), the answer is saying that the result from voluntary would become different from the mandatory national census, due to participant differing in demographic characteristics.
However, I think for C) to stand, it needs further assumption that mandatory census was indeed representing the majority of population so differing away from it would logically mean lower participation rate or less accurate. What if the mandatory census had so much lower participation rate, say 20% but voluntary lures somehow bigger participation rate 50%? If the previous 20% had demographic, say, skewed toward older generation and less representative as the sample, the fact demographic being different could actually make the result more accurate.

B), which I chose to be better suited, makes the case that anyone who hadn't participated in the mandatory poll would not participate in the voluntary so voluntary poll can't be more participated. This assumption is more necessary than C).

[Rachael Wilkenfeld]

Hi Silver,

We know that the participation rate for voluntary is lower per one of the premises. The premise says "If the census becomes voluntary.....the participation rate would be lower." We accept the information in the stimulus, but not the logic or conclusion drawn by the pollster here.

The key here is that to say that the results are less accurate, we need to know there's a different demographic. It wouldn't be less accurate if it's demographically the same as the mandatory poll. It would be the same accuracy because it's the same demographically compared to the mandatory poll.

In regards to answer choice (B), we don't need that information. As explained in the first paragraph, we don't need an assumption supporting that the voluntary census would have fewer participants. We already know that from the stimulus. Instead, we need to know that when the participation drops, it's a different demographic population answering the census.

Hope that helps!
Rachael

[lsatlies]

But this assumption still fails to make the conclusion valid, because it could still be the case that the mandatory census with the higher participation rate was skewed in one way or another, and that the voluntary census, despite having lower participation rate and different demographics, happens to be MORE accurate to the general population. So C is not operative, nor does it actually validate the conclusion. Particularly egregious case of the LSAT negating a correct answer (author is assuming census data is the only way opinion polls can get results) and then selecting a "correct" answer that, upon closer inspection, is wrong.

[Jeff Wren]

Hi lsatlies,

You're correct that Answer C does not make the conclusion valid for the reason that you've stated.

I can't tell from your comment whether you're mentioning this as a criticism or problem with Answer C?

Just to be clear, this question is asking for an assumption that is necessary for the argument, not for an answer that makes the conclusion valid, which we classify as Justify the Conclusion questions.

Although there are times where necessary assumptions also do make the conclusion valid (i.e. an answer is both sufficient and necessary for the conclusion), more often they do not.