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Reverse Causation in GMAT CR

Posted on September 17, 2013

Assumption-based questions make up about 40% of the questions in GMAT CR. They test you on your ability to identify and understand the relationships – if any – that exist between the premises and the conclusion. Some of the tricky logical traps that assumption-based questions may contain are based on causality.

 

Today, we will look at Reverse Causation in GMAT CR.

 

Causation means that one event triggers or causes another. The direction of this causation (does X cause Y or vice versa?) is the trap that GMAT sets. Let me take an example:

 

Every day, at 9AM, Ramu the peon rings the school bell and Mrs.Mathews, the Principal, comes out of her room for the school assembly.

 

There are 2 events hereBoy_Thinking_1

 

Event X: Ramu rings the bell

 

Event Y: Mrs. Mathews comes out of her room

 

From this, can we assume that Mrs.Mathews comes out for the assembly because she heard Ramu ring the bell? i.e. can we assume that X is causing Y? It does seem reasonable, doesn’t it?

 

Now, think about this in a different way: Every day, at 9AM, the punctual Mrs.Mathews comes out for the assembly, and upon seeing her, Ramu the peon rings the bell. Also plausible? 🙂

 

This means that Y could be causing X.

 

Thus, a causal relationship exists between X and Y, but its direction needs to be evaluated.

 

Now let me take a GMAT CR question:

 

A researcher discovered that people who have low levels of immune-system activity tend to score much lower on tests of mental health than do people with normal or high immune-system activity. The researcher concluded from this experiment that the immune system protects against mental illness as well as against physical diseases.

 

The researcher’s conclusion depends on which of the following assumptions?lightbulb

 

The argument‘s conclusion is that ISA impacts mental health. We need to identify the underlying assumption. The correct answer to this question is option D: Mental illness does not cause people’s immune-system activity to decrease. This is a classic case of reverse causation.

 

Let us negate option D: Mental illness causes people’s immune system activity to decrease. If this were to be true, it means that mental illness impacts ISA and not vice versa. i.e. Y is causing X and not the other way round. This breaks the argument – since negation breaks the argument, option D is the right answer.

 
 

Key Takeaway

 
Whenever you see a cause-effect relationship between 2 events on a GMAT CR question, question its direction. Do not take for granted the direction apparently given in the question stem.
 

Direction

 
 
Hope these techniques make a positive difference to your GMAT prep! If you’d like to share what works for you and what doesn’t, please leave a comment in the comment section below.
 
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