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PrepTest 73, Logical Reasoning 1, Question 13


Question 13. When a question asks for the flaw in an argument, not surprisingly, we call that a flaw question. And on a flaw question, our job is to find the error in the argument. But of course, before we can find the error in the argument, we need to understand its conclusion and its evidence.

The conclusion of this argument comes at the very end. This demonstrates that putting more people in prison can't help to reduce crime. The evidence for that is basically two parts. First, there was a survey. The survey was of police departments, they kept track of the national crime rate. And they found that the annual number of crimes per 100,000 people hasn't changed over the last 20 years.

But, second piece of evidence at the same time, the percentage of people in prison has gone up and the spending on prisons has gone up. So the the reason that putting people into prison can't help to reduce crime is that you put some people into prison, and it doesn't seem to have reduced crime. So, what is the flaw in this argument? Well, there are a couple of flaws that this argument avoids.

The first is, a percent versus number flaw. Notice that the crime rate is not about the number of crimes committed. It's the number of crimes per 100,000 people. Similarly, a lot of arguments have inadequate samples or some sort of sampling error. Anytime you've got an argument based on a study, you should think about the sample.

But here, it's a pretty big sample. It's the national crime rate through police departments, presumably nationwide. But that doesn't mean anything wrong with the sample. Instead, the error here is a concept shift between, the idea of helping reduce and reducing. We know that crime rates haven't gone down.

But does that mean that the prisons aren't helping to reduce crime? Could it be true, that is, it could be that the prison population isn't helping in any way. But it could also be true that the prisons are helping keep the crime rate at the current rate, that without those prisons, the crime rate would be going way, way up more quickly.

Just because things are staying even doesn't mean that nothing is helping, imagine that you're in a boat, somebody is throwing buckets of water over the edge because there's a leak. If the boat is staying where it is in the water, that doesnt mean that the guy bucketing the water out isnt doing something. If not for the bucket, maybe the boat would sink.

So, let's see what we've got in the answer choices. The first answer choice is meant to hint at the percent versus number flaw that the original argument avoided. It says that it refers to our justification that because the national crime rate has increased, that the number of crimes has increased. But this argument carefully set itself to the percent of crimes, that is, crimes per 100,000 people.

So it's not committing this error, answer choice B, well, this is what we were looking for. Ignores the possibility of the crime rate would have been increased, if it had not been for the greater rate of imprisonment. So, what would have happened if we hadn't been putting in people into prison? That's the of the issue.

So answer choice B is our answer. So why are the other answer choices wrong? Well, answer choice C, overlooks the possibility the population has increased significantly over the past 20 years. This is another version of that percent versus number flaw. The argument was just about crimes per 100,000 people.

So if there's a lot more people, that wouldn't change, crimes per 100,000 people. If you have a million people or 2 million people, it doesn't change the crimes per 100,000 people. Answer choice D, this argument never talks about alternative methods. It's just saying that prisons aren't working.

So whether other methods would work is outside the scope of this argument, and then answer choice E, takes for granted the number of prisoners must be proportional to the number of crimes committed. Once again, we could say this argument narrowly avoids a percent versus number issue by tagging this to the crime rate, not the number of crimes. Also, I mean it doesn't assume anything about where the numbers ought to be, whether they ought to be proportional or not.

So hence, choice E is not something that's wrong with this argument, the answer is answer choice B.

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