GMAT Critical Reasoning vs Data Sufficiency: Two Sides of the Same Coin

Traditional GMAT wisdom suggests that the skills needed for success on the Verbal section overlap little, if at all, with one’s quantitative abilities. Given our educational system and the very fact that the GMAT has separate Quantitative and Verbal sections, such a distinction seems uncontroversial and downright obvious. But, as we all know, the structure and content of the GMAT can often run against our common-sense intuitions. Yes, the different GMAT sections assess the skills that fall within the designated domain (you certainly won’t see any Word Problems in the Verbal section), but, sometimes, the skills tested on GMAT Critical Reasoning are almost identical to the Quantitative intuitions tested on Data Sufficiency. In fact, I’d go so far as to argue that GMAT Critical Reasoning and Data Sufficiency test almost the exact same skills, just in different contexts: at their core, both question-types are concerned with a test-taker’s ability to take given information and assess how it impacts a certain conclusion. To get a sense of this similarity, let’s take a look at a sample Critical Reasoning question and how it can be phrased as a data sufficiency question (note, this question comes from test #1 on the GMATPrep Software):

The violent crime rate (number of violent crimes per 1,000 residents) in Meadowbrook is 60 percent higher now than it was four years ago. The corresponding increase for Parkdale is only 10 percent. These figures support the conclusion that residents of Meadowbrook are more likely to become victims of violent crime than are residents of Parkdale.

A. changes in the population density of both Parkdale and Meadowbrook over the past four years
B. how the rate of population growth in Meadowbrook over the past four years compares to the corresponding rate for Parkdale
C. the ratio of violent to nonviolent crimes committed during the past four years in Meadowbrook and Parkdale
D. the violent crime rates in Meadowbrook and Parkdale four years ago
E. how Meadowbrook’s expenditures for crime prevention over the past four years compare to Parkdale’s expenditures

Let’s first break down the argument. We have two given pieces of information:

#1: Over the past four years, the crime rate in Meadowbrook increased by 60%.
#2: Over the past four years, the crime rate in Pardkale increased by 10%

Using this information, the argument erroneously concludes “that residents of Meadowbrook are more likely to become victims of violent crime than are residents of Parkdale.”

So what’s’ the flaw? Notice that the given information concerns percentages. Meadowbrook’s crime rate increased by 60% and Parkdale’s crime rate increased by 10%. From this information on percentages, the argument commits one of the GMAT’s favorite mathematical assumptions: conflating percentages with actual values. Yes, the percentage increase was greater in Meadowbrook than in Parkdale, but what we don’t know is the actual crime rate in the two regions before the increase. Perhaps Meadowbrook’s original crime rate was 10, and Parkdale’s was 10,000. In this case, after the different increases, the crime rate in Parkdale (10,000 * 1.1 = 11,000) will still be greater than that of Meadowbrook (10 * 1.6 = 16), even though the percentage increase was greater in Meadowbrook. Thus, the flaw in the argument is that it fails to account for the crime rates in the regions four years ago. The correct answer is thus D. For the purposes of this blog, what’s particularly noteworthy about this question is that it can just as easily be worded as a yes/no Data Sufficiency question. Look at the following:

Is the crime rate in Meadowbrook greater than the crime rate in Parkdale?

1) Over the past four years, the crime rate in Meadowbrook increased by 60%.
2) Over the past four years, the crime rate in Parkdale increased by 10%.

Notice how similar the prompt is to the conclusion in the CR question. The only major difference is that, in the CR question, the conclusion was presented as true, and we wanted to find evidence that would call it into question, whereas in this DS question, we’re trying to assess whether the conclusion is definitively true, based on the information in the statements. What’s interesting is that, in both cases, the fundamental issue is the same: the erroneous assumption that a greater percentage increase corresponds to a greater value. In this DS question, the answer is E for the very same reason that the answer was D in the CR question: we simply do not know the initial crime rates for the two regions, and without this information, the conclusion cannot be properly drawn.

More than anything, the above examples reinforce the point that the GMAT is, above all, a reasoning test. Though there are indisputable differences in Quantitative and Verbal reasoning, the general thought process for Critical Reasoning and Data Sufficiency questions is quite similar: understand the given information, understand the conclusion that you’re trying to address, and consider the assumptions necessary to reach the given conclusion.