Assuming that bases are same on GMAT Critical Reasoning

Assuming Bases are the Same on CR

In GMAT critical reasoning, there are several different types of questions that you will encounter. In this short article, we will cover the characteristics of questions involving comparison of the effects of a given event on two sample sets and how to solve them.

Incorrect Analogies

One type of fallacy found in GMAT CR questions is assuming that bases are the same. This fallacy occurs when post-event differences on a sample are attributed to the event, without first establishing that the pre-event results were similar.

Please take a close look at the following example to understand this concept.

Example 1: Over a period of three months, Group A was given the tonic Xinca. Group B was given a placebo. Post experiment, members of both groups were given the same IQ test; Group A performed significantly better than Group B. Xinca improves intelligence

Can you identify what the flaw in this reasoning is?

The flaw is that it has not been established that the two groups had similar IQs before the experiment.

Let u now take a look at a GMAT-like example.

Example 2: Group 1 was shown a movie with 30 scenes in which an actor smoked a cigarette. Group 2 was shown a movie with no such scenes. Within one hour of seeing their respective movies, 40% of Group 1 members took a smoke, whereas only 20% of group 2 members did so. The experiment establishes that seeing actors smoke in a movie instigates one’s instinct to do so.

Which of the following pieces of information would be most necessary for evaluating the validity of the described experiment’s conclusion?

Here, we have an argument followed by a question stem.

Step 1 – Look at the question stem.
Step 2 – Read the reasoning.
Step 3 – have a broad expectation from the correct answer choice.

So, the pieces of information needed to determine the validity of the results is whether the bases were the same before the experiment. Look at this answer choice:

Option 1: Whether the members of Group 1 and Group 2 were equally susceptible to smoking before the experiment.

This is the correct answer choice.

This article has deliberately been kept brief; for a more elaborate explanation, please refer to the Experts’ Global Stage One Critical Reasoning videos.