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LSAT Logical Reasoning Tips: June 09, Sec 1, #20 -or- Speed Limits on the Highway Suck for More Reasons Than You Think


I got my hands on the June 2009 test pretty recently. As that is the most recent LSAT that anyone will see before the upcoming September exam, there are always important lessons to be learned from such a recent test. As for me, I am taking the September test that will be my first real administered LSAT since 2006. When you teach the LSAT for a living, you tend to familiarize yourself with all of the questions. There is no such thing as an LSAT question that I have not seen. So basically I have no way to study. (I know; it’s a big problem). Except, of course, for the June test. So I was thrilled at the opportunity to take a new LSAT. Yes, I am aware that this is slightly lamer than owning a ShamWow, subscribing to eHarmony, or dotting an i with a heart.

As I was working through the Logical Reasoning on the exam, I inevitably started searching for teaching points as much as correct answer choices. So I decided that I would share some of the valuable lessons that can be easily uncovered in the June test. I am going to write a sequence of blog entries that will break down five or so Logical Reasoning questions from the June 2009 LSAT. (You will be able to purchase the entire test from LSAC some time in July.)

Remember, the big trick on the LSAT is to take what we call “meta-points” from questions. You will not see the same question on your LSAT, unfortunately, but you will have questions that require the same mental maneuvers and you will see incorrect answer choices that will prey upon common mistakes.

Alright, here we go. Note: I have to slightly alter the questions due to licensing issues but the gist is the same.

June 2009, LR1, #20

The first thing that you should always do is read the prompt and classify what type of question you are attempting.

    Which one of the following, if true, most seriously weakens the argument?

So here is what we know. We are going to see an argument in the stimulus and it is our job to find an answer choice that weakens this argument. In your mind, you should thus be looking for a weakness in the argument as you read through, so that you can then exploit that weakness in an answer choice.

Below is the stimulus. Read through this slowly and try to comprehend what the argument is trying to prove, how they are attempting to prove it, and attempt to spot any weaknesses in the argument.

    Prior to a certain year, when there was no highway speed limit in Los Angeles, the highway accident rate increased yearly, peaking a decade ago. At that time, the speed limit on highways was set at 65 miles per hour. Every year since the introduction of the highway speed limit, the highway accident rate has been at least 15 percent lower that that of its peak rate. Thus, setting the highway speed limit at 65 mph has reduced the highway accident rate by at least 15 percent.

And there we are. First things first, this argument is completely ridiculous to anyone who actually lives in Los Angeles. If you have ever hopped on the glorious 405, you quickly realize that a speed limit on freeways in LA is about as useful as birth control is to the Palin family. We always drive 12 mph unless we are stopped outright. Then we just start shooting at each other in frustration.

Back to the question. This is a very common form of argument in Logical Reasoning. First, you are presented with a correlation. Before there was a speed limit, there were lots of accidents. After a speed limit was imposed, there were fewer accidents. Correlations are very common on the LSAT, and they very commonly set the foundation for a big fallacy that we see here. In this argument, a correlation is taken to imply a much stronger relationship: causation. The conclusion actually asserts that the imposition of the new speed limit is responsible for, or caused, the reduction in the accident rate.

In such a situation, there is always one thing that you should be thinking: It could have been caused by something else. Causation is very hard to establish. So even if it seems likely that the speed limit did decrease the accident rate, you can always weaken that conclusion by raising another possibility. So let your mind wander briefly about what other factors could have stopped people from running into each other. Maybe LA instituted a policy of mandatory driver training? Maybe LA prohibited all alcohol consumption within the city limits? Maybe the driving age was raised to 21 so the crazy teenagers are off the road? The possibilities are endless, but that should be your mindset.

If you think about it, the reasoning in this argument is as simple as in the following argument:

    I used to not get many dates. Then I started using AXE deodorant body spray on a daily basis and my social calendar is now completely booked. AXE must have made the difference for me.

Well, not necessarily. We fall prey to this type of reasoning in everyday life, and we are often presented with it in advertisements (like the compelling ad above). Of course, it could be possible that something else led to my sudden increase in dates, like puberty, or money, or possibly dropping my standards.

There are a few other things to notice here.

First, note that the argument concerns the accident rate. There is a big distinction on the LSAT between statements based in numbers and statements based in percentages. Saying that the fatality rate for base jumping is higher than the fatality rate for crossing the street does not necessarily mean that more people die of base jumping than crossing the street. In this question, we are dealing with the accident rate, so that would be independent of the number of drivers on the road. This is always important to keep in mind. They could give you an answer choice that says that more people are utilizing public transportation since the new speed limit was put into place (yeah, right, this is LA). That would be a very tempting answer choice but actually would be irrelevant because we are only dealing with the accident rate and not the total number of accidents.

Second, always track the conclusion, as it is the most important part of the argument. Here, it says that the speed limit has reduced the accident rate by at least 15 percent. That is an incredibly strong claim. They are not just saying that the speed limit is partially responsible for the change in the accident rate, but that the speed limit is entirely responsible. Thus, to weaken the conclusion, we just have to find some other option that could account for part of that 15 percent decrease.

Finally, always watch for the scope of the argument. Here we are just talking about highways in Los Angeles. So the accidents that occur on the side streets or in alleys or parking lots would not be relevant. Additionally, information about other cities would not be relevant unless they bear a strong relationship to LA (Chicago, maybe, Des Moines, no).

Excellent. Now that might seem like a lot, but this is the key. You have to be able to notice the little tricks that are commonly introduced. If you can do this sort of analysis (and do it in roughly 30 seconds), you will never get a question wrong.

Now we examine the answer choices. For each one, try to think about whether it weakens the argument.

    (A) In the years prior to the introduction of the highway speed limit, many cars could go faster than 65 mph.

Wow, say it ain’t so. There were cars that could go faster than 65 mph? Those people must have been scared for their lives. Flying along at 68 mph? While this is both fascinating and scary, this tells us nothing about the effect of the new speed limit.

    (B) Ten years ago, at least 95 percent of all automobile accidents in the area occurred on roads with a speed limit of fewer than 60 mph.

So this answer choice says that nearly all of the accidents that occurred before the new speed limit did not happen on the highway. But we already said that this is irrelevant. The proportion of accidents that take place on or off the highway does not matter. We just need to know why the accident rate on the highway went down.

    (C) Although the speed limit on many highways is officially set at 65 mph, most people typically drive faster than the speed limit.

This one is tempting. Here is what they want you to think. Oh, so people don’t obey the speed limit and that means that the speed limit could not have been the reason why the accident rate went down. But that would be a mistake. This argument does not state anywhere that people all drive under the speed limit. Maybe everyone now drives 70 mph but that is still much slower than they used to drive. Or maybe the speed limit did not dramatically change the speed that people drive, but it sill makes them drive more safely because they know that there are restrictions in place. So be careful, this one does not weaken the argument.

    (D) Thanks to changes in automobile design in the past ten years, drivers are better able to maintain control of their cars in dangerous situations.

Now, think about this one. The time frame is right because it focuses on the last ten years (since the speed limit was introduced and after there was the peak in the accident rate). If it is the case that car manufacturers are producing safer cars, then that could also account for the decrease in the accident rate. If all of the cars on the road have better brakes or give drivers better control and more ability to avoid accidents, then this could have dropped the accident rate, whether the speed limit was reduced or not. Since this gives us another factor that could account for the accident rate other than the speed limit, this answer choice weakens the argument.

One quick problem that students sometimes face. Yes, but couldn’t the speed limit still be responsible? It could be, but that is not the point. Even though the speed limit change could still have been responsible for some, most, or even all of the drop in the accident rate, raising the changes in automobile design as another alternative weakens the support for that conclusion. On a question like this, you do not have to annihilate the conclusion; you just need to weaken it. It will seldom be the case that you can prove that a conclusion is false, but rather you just have to prove that it is less likely to be true.

    (E) It was not until shortly after the introduction of the highway speed limit that most cars were equipped with features such as seat belts and airbags designed to prevent harm to passengers.

This is also a very popular answer choice. However, there is an easy way to dismiss this as an option. The argument here has to do with the accident rate, so we are concerned with how many people get into automobile accidents. This answer choice is concerned with what happens after an accident takes place. Do the passengers get injured or not? We hope not, but whether the passengers get a bruise or lose a limb actually doesn’t affect the fact that there was an accident in the first place.

After our analysis, it is hopefully clear that you should choose answer choice (D) and move on with confidence. This illustrates just how much you can learn from one Logical Reasoning question. The LSAT is very good at hiding the concepts that they like to test, but if you really analyze a question you can start to see how this test really works.

So keep breaking down those arguments and I will be back soon with another installment. For now, I am going to lower my standards as I slather myself with some AXE.