Monday, March 8, 2010

Logical Reasoning Zen Task Standard: Resolve Discrepancy

As we mentioned, during the spring we'll be going through the 22 different Zen task standards on the logical reasoning section of the LSAT. We feel that this LSAT classification system is more comprehensive than other methods of categorizing the section, as it not only breaks down the section by question stem, but how to perform the task to receive credit.

For today we'll explain how we approach one of the tasks, resolve the discrepancy, which is where the LSAT asks you to choose from a list of possible explanations the one that best explains two seemingly contradictory elements from the stimulus.

While this task is prompted by several different question stems, as exemplified by the sample one we chose below, the LSAT has, in general, codified their question stems since 2007. On modern LSATs, the most common versions of this question stems are:

Which one of the following, if true, most helps to explain the difference between [piece 1 of stimulus] and [piece 2 of stimulus]?

Which one of the following, if true, most helps to resolve the apparent [discrepancy] described above?
These two different structures also often correspond with different stimulus structures, with the former for lengthier stimuli--with lots of evidence--and the latter for short stimuli with conflicting principles.

The key to correctly answering a resolve the discrepancy question is to highlight the two conflicting portions of the stimulus and prephrase the type of evidence needed to explain their relationship. As with depends upon assuming, the goal is not to describe the specific evidence--as the LSAT answers will invariably mention the "correct" parts--but rather the gap in relationship between the two pieces of the stimulus

The example we chose for this task is taken from the Sample Questions with Explanations document on LSAC's website. You should be actively reading the stimulus and marking it with both highlighter and pencil, focusing on identifying the two different pieces of the stimulus and their relationship. If the question stem is of the lengthier variety, actively marking the stimulus should be much easier as the LSAT has already spelled out the two conflicting pieces.

The orange highlighted text of the question stem is a fairly standard version of the modern LSATs. The LSAT tells you to pay attention to the two different ways the Romans used--or didn't use--water power in their empire, specifically in outlying parts and large cities, respectively.

The correct prephase after reading the stimulus should be something along the lines of:

I need evidence that shows why it was harder to use water power in cities than in outlying provinces.
Or, the contrapositive:
I need evidence that shows why it was easier to use water power in outlying provinces than in cities.
Answer choice E mentions all the necessary evidence in the correct relationship from the prephrase. It describes how in one of the regions from the stimulus, the cities, the extensive use of water power would cause a negative reaction, social unrest, which would not occur in the outlying provinces.

Note that there are thousands of possible reasons why the Roman cities might not depend on water power; the specificity of this answer with social unrest as the cause is a perfect example of why it's impossible to prephrase the answer choice. The distractors below all have relevant pieces of evidence, they are just presented in the incorrect relationship.

Distractor choice A mentions the large cities, but provides us with a reason why water power should have been feasible for them. Thus it is exactly the opposite of what we're looking for.

Distractor choice B is similar to choice A in that it mentions the cities and then quickly tells us that there was substantial water throughout the year. "Some seasonal variation" is not nearly strong enough of a negative to provide the explanation we're looking for.

Distractor choice C starts out promisingly, describing how water power could be disrupted--and thus cause more problems if more people depended upon it--but then turns 180 degrees and explains why it's not worth worrying about.

Distractor choice D indirectly mentions the cities, but then introduces evidence which is irrelevant to the differences in use of water power.

Below is the frequency that this task has been asked on modern LSATs and the percentage change in frequency from pre-2007 LSATs. It averages 4.8% of the points on a modern LSAT, and you can reasonably expect that two points will be devoted to resolving discrepancies.

18 times
on LSATs since 2007
4.8% of LR
(~2 per LSAT, range 1-4)
0.2% growth from pre-2007
According to LSAC:
This was a “very difficult” item. Approximately one third of test takers answered it correctly when it appeared on the test.