Monday, March 5, 2012

Logical Reasoning: Most Strongly Supported by [Stimulus]

Today we'll explain how we approach one of the tasks, most strongly supported by [stimulus], which is where the LSAT asks you to extrapolate a new piece of evidence by combining the information presented in a stimulus.

This task is prompted by fairly pedestrian and easy to identify question stems, and the only difficulty should lie in carefully distinguishing them from strengthen tasks. On modern LSATs, one of the most common versions of this question stem is:
The statements above, if true, most strongly support which one of the following?
Most strongly supported by [stimulus] is the "loosest" of the extrapolation standards, in that the correct answer choice can be further afield from the evidence presented in the stimulus. For example, the correct answer may apply the evidence to a new situation or make an analogy, whereas the infer task requires you to draw a conclusion solely from the information presented in the stimulus. In order to correctly identify the inference, you will be required to read between the lines more than is required for the more concrete task.  

However, the general strategy for all extrapolation strand task will serve you well for most strongly supported by [stimulus]. Thus, the key is to clearly highlight the main pieces of evidence--focusing on the actors and their definitions--and how they can be combined in terms degree, certainty, and opinion.  As with depends upon assuming, the goal is not to describe the specific evidence--the LSAT answers will invariably mention the "correct" parts--but rather the links that create the relationships and the degree of certainty between those pieces.

Once you have identified these qualitative links between actors and how certain you are about each link, you should prephrase what information you do know and highlight what you don't know. Often the correct answer choice will hinge on either the relationships between the actors or the degree of certainty, but the most difficult most strongly supported by [stimulus] questions will play with both axes and introduce extraneous actors in the distractors.

Common distractors for this task include answers that make claims that are unwarranted based on what is presented about the actors/relationships/degrees of certainty:
  1. Actor: introducing a new topic and treating it as though the stimulus' evidence applies to it.
  2. Relationship: linking two or more actors in a way that is not supported by the stimulus, i.e., claiming that one causes the other.
  3. Degree of certainty: making claims that are too strong, i.e., "too certain," or too weak based on the key language in the stimulus.
For example, consider this stimulus: 
A virus can infect birds and mammals, but only through mosquitoes; while humans sometimes are infected, they cannot transmit it to new mosquitoes. The virus originated in one region and only recently migrated across the world.
In this simplified example, we should clearly identify the actors, the relationships between then, and how certain we are about each link.
  1. Actors: birds and mammals (with subset of humans), virus, mosquitoes, and two world regions
  2. Relationships and degree of certainty
    1. birds and mammals can contract virus, but only through mosquito bites
    2. humans can sometimes catch the virus
    3. humans can never pass the virus to mosquitoes
    4. the virus definitely passed from one region to the next in the recent past
A correct answer might be to combine the impossibility of humans passing the virus on to each other and the recent migration between the regions: that is, that humans could not have been the carrier for the virus, because an infected person can't pass it on to other birds or mammals (only through mosquito bites), and a human could not have passed it to a mosquito intermediary.

Distractors for this stimulus might include 
  • a prediction about the future spread of the disease (no temporal relationship on which to base predictions)
  • present mosquito population size as strict correlation with prevalence of the virus (relationship only for mechanism of transmission)
  • severity of the virus on human health (relationship only for mechanism of transmission)
  • comparing the two regions in infection rate (only temporal relationship between regions)
In this example, the actors are in black, the qualified relationships are in red arrows, and the degree of certainty is in cyan.
In the above diagram, a correct answer choice might say that beginners can reduce their change of injury by not trying to do the exact same kicks as experts. This example flips a line of relationships by stating its inverse relationship: the stimulus describes what happens if beginners do try, and the answer choice extrapolates what would happen in the absence of that relationship.

Note that the stimulus presents many information that is not addressed in the answer choice; this is obviously not a problem, but it is often a source of confusion for LSAT students. Inversely, the problem of  being "out of scope" is much less in this task, as answer choices can travel far afield from the explicit topics of the stimulus and still accurately reflect its relationships and degrees of certainty with new actors.