GMAT Weaken CR: Correlation vs Causation | OG | Volunteer Work

In GMAT Critical Reasoning, many arguments conclude that one thing causes another from nothing more than an observed pattern, and this easy Official Weaken question, which begins “People who do regular volunteer work tend to live longer,” is a clear example of how to handle that move.

Some arguments show you two things that tend to occur together and then conclude that one causes the other. If you catch that move while reading the passage, you will already know what the correct answer is likely to do before you reach the choices.

Start with the standard every correct weakener must meet: it brings in a new piece of information that reduces your belief in the conclusion, without challenging any premise.

The Question

In this question, people who do regular volunteer work tend to live longer, on average, than people who do not. Doing good, a category that includes volunteer work, releases endorphins, which induce a feeling of well-being.

The author concludes that regular releases of endorphins must in some way help extend people’s lives.

From correlation to cause: two gaps to check

Look at what the premise gives you. It is an observation: regular volunteers live longer than others. That is a correlation, and you cannot challenge it. The conclusion turns it into a cause: volunteering releases endorphins, and the endorphins extend life.

Whenever an argument moves from a correlation to a cause, keep two gaps in mind:

Reverse causality. What if the arrow points the other way? Instead of volunteering making people live longer, people who were already likely to live longer may be the ones who take up volunteering.
A third cause. What if something not mentioned in the argument leads people to volunteer regularly and also helps them live longer?

There can be other gaps, but these two should come to mind every time.

What the correct answer must do

Read the question stem carefully. It asks what undermines the force of the evidence given as support for the hypothesis. The evidence is the longer lives of volunteers. So the correct answer needs to bring in new information suggesting that their longer lives are not because of endorphins. It does not need to prove that endorphins do nothing.

The correct answer

The correct choice says that people tend not to become involved in regular volunteer work unless they are healthy and energetic to begin with.

This is reverse causality. Good health and energy come first, and they are what bring people into regular volunteering. Those same healthy, energetic people may live longer anyway. So the volunteers’ longer lives may reflect the health they already had, not anything the volunteering or the endorphins did for them. The observed pattern now has another explanation, and it no longer supports the endorphin hypothesis.

Notice that this choice never mentions endorphins. It does not need to. It removes the reason to believe endorphins were behind the pattern in the first place.

Why a similarity cannot explain a difference

There is one more way to see why this choice works. The evidence compares two groups: regular volunteers and everyone else. One group lives longer. To explain that difference another way, a choice has to point to a difference between the two groups. The correct choice does exactly that: the volunteers were healthier to begin with.

Compare it with choice (A): people who do regular volunteer work are only somewhat more likely than others to describe the work they do for a living as “doing good.” This tells you the two groups are similar on this measure. A similarity cannot explain why one group lives longer than the other.

The habit this builds

When an argument draws a cause from a correlation, ask yourself:

Is the conclusion assigning a cause to something that was only observed together?
Could the cause and effect run the other way?
Could something else be causing both?
If the evidence compares two groups, does this choice point to a difference between them?

This habit is not limited to Weaken questions. On Strengthen, the correct answer often rules out reverse causality or a third cause. On Assumption, the author is assuming that neither of them is at play. On Evaluate, the correct answer often asks whether one of them is true. Spot the correlation-to-causation move once in the passage, and you know what to look for in all four question types.

About the Weaken Beginner Series

This question is part of the Weaken Beginner Series, in which easy Official GMAT questions are used not to test what you know, but to reveal how you think. Each question targets a specific reasoning habit, one that shows up in a simple form on easy questions and a complex one on hard questions. If you are getting started with Weaken questions or if Weaken questions feel inconsistent for you, this series is built to show you exactly where the process is breaking down.

Correlation Turned Into Causation: Two Gaps to Check Before You Read the Choices