Causation in Critical Reasoning Questions
A few weeks ago, we covered the topic of Math in Critical Reasoning Questions (click on the link to read the article), brought to us by Chris Ryan, Manhattan GMATs Director of Instructor and Product Development (not to mention one of the people I admire most in the GMAT world). Weve got another great installment from him this week, this time on the concept of causation in Critical Reasoning questions.
The concept of causation appears regularly on the GMAT and most people taking the exam can expect to see at least one Critical Reasoning question dealing with the issue. If you understand the concept and anticipate it, you will be much better prepared to answer the question correctly when it arises.
First, in general, causation means that one thing causes another thing to occur. (Its also possible, of course, for several things to combine to cause one thing to occur, for one thing to cause several things to occur, and so on.)
Two problems generally crop up when the GMAT tests the concept of causation. The first is a false assumption that the causal connection is possible in one direction only. What does that mean? Causation is, as the term implies, a direct causal link: x causes y.
So, whats the problem? Well, theres also another concept we need to know, something called correlation. Correlation is essentially coincidence: x and y occur together so often that a causal relationship is assumed. For example, Ive noticed that every time people are walking around outside with umbrellas, the ground is wet. Which one causes the other?* When two things occur together, how do we know whether x causes y or y causes x or whether neither causes the other? (* Neither theres a third thing that causes both of those events to occur. :))
Let's look at another example: Imagine that every time a bee lands on a certain closed flower, the flower opens and the bee enters to gather pollen. It would be easy to assume that the bee's landing somehow spurs the flower to open. It is equally plausible, though, that the flower's opening causes the bee to come land on it. That is, the bee might know when the flower is about to open through some special bee intuition and then arrive just in time. The causal connection (between the bee's landing and the flower's opening) cannot be proven in either direction from this simple observation. All we know for sure is that the two events are correlated.
How does this play out on the GMAT? Imagine the following Critical Reasoning argument:
Researchers have noticed that people whose blood shows abnormally low levels of calcium usually develop laryngeal polyps, which can permanently damage vocal cords and result in partial or even total loss of voice. In order to prevent the polyps, the researchers recommend a diet high in calcium-rich foods such as dairy and green, leafy vegetables.
Does the argument provide a clear causal connection between low levels of calcium in the blood and laryngeal polyps?
Reading the above argument, we are tempted to take for granted that there is a causal connection: lack of calcium -> laryngeal polyps. But it is equally plausible that laryngeal polyps -> lack of calcium. How? Imagine that the polyps somehow prevent the body from processing calcium, so that it is not the lack of calcium causing the polyps but rather the polyps that cause the lack of calcium. In the latter case, increasing one's dietary intake of calcium would likely do little to combat the polyps. (And theres also the possibility that theres no causal connection between these two events at all.)
The second major problem with causation on the GMAT is the assumption that there are no alternate models of causality. That sounds a lot more technical than it really is. Essentially, this occurs when one assumes that there is only one possible cause of a certain outcome. For example, "The ground is wet, therefore it must have rained."
In this case, the faulty assumption is that only rain could have caused the ground to become wet. It ignores the possibility that someone could have spilled a bucket of water, someone's sprinklers could be on, a garden hose could be leaking, etc. In the absence of direct proof of causation, one cannot assume that any particular thing is necessarily the cause of a particular outcome. How does this play out on the GMAT? Consider the following argument:
The recent boom in new home construction has finally begun to taper off. Developers are not buying land, contractors are finding themselves going without work for longer periods, and banks are issuing fewer mortgages. People must not want to buy new homes as much as they wanted to even six months ago.
Is this conclusion ("People must not want to buy new homes as much as they wanted to even six months ago.") valid? It might be true, but must is too strong. It may be, for example, that all of the observations made in the argument were caused by a steep increase in interest rates or unemployment, so people dont have the necessary funds to buy a home even though they want to buy a home as much as ever. If this is true, then we have an alternate cause: lack of money.
Whenever a claim of causation is made in a GMAT Critical Reasoning argument, you need to consider (a) whether the relationship is causal or correlative; or (b) whether there are other possible causes for that particular outcome.
Major Take-Aways from Chriss Article:
- When you see language that indicates some kind of causal relationship, especially in the conclusion, review the argument carefully. What do the premises actually establish as far as the causal relationship?
- Did the argument actually provide proof of the causal direction (x causes y)? Or is the conclusion assuming a causal relationship after providing evidence of a mere correlation (x and y occur together)? If the latter, then look for a choice that discusses how y might or might not cause x.
- Did the argument actually provide proof that there was only one possible cause for the given outcome (x causes y)? Or does the argument make an assumption that theres only one cause when there may actually be other possible causes (perhaps z causes y)? If the latter, then look for a choice that discusses how z (a different cause) might or might not cause y.