Logical reasoning PrepTest 120 · Section 1 · Question 19

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
The OPV causes the only new cases of polio each year in North America. The IPV would cut that number if half. Therefore, North America should switch from OPV to IPV.

Answer Anticipation:
The stimulus makes a recommendation to switch from one option to another. This is based on a single point of comparison—the switch would cut the number of vaccine-caused polio each year in half.

Whenever an argument makes a recommendation, check to see if the criteria by which the decision should be made is established, and if the options are all analyzed over the criteria.

Here, no criteria is established. It's suggested that the number of new cases each year is the relevant criterion, but then it only discusses the number of vaccine-caused cases, when the stimulus also brings up naturally occurring cases. So the criteria the argument seems to assume is the relevant one isn't even established!

Since the recommendation is based on only a single pro, there could be any number of cons that would suggest that switching might be a bad idea! An answer tied into the assumed criteria (potentially dealing with an increased number of naturally occurring cases if the switch is made) would weaken this argument, but so would any other answer that suggests the cons of the switch would outweigh the listed pro.

Answer Explanation:
This answer establishes that the switch will have a downside directly related to the pro listed for the switch—more naturally occurring cases. And since the upside was reducing 12 cases to about 6, and few new cases of naturally occurring polio is enough to call the wisdom of this switch into question. This answer therefore weakens the argument.

Key Takeaway:
When an argument makes a recommendation, check to see if it establishes the criteria by which that recommendation will be made, and if it explores that criteria for all options.

Incorrect. Giving immunodeficient children polio is probably something to be avoided, and if the switch can make that happen, then we should probably do that! If anything, this strengthens the argument.

Incorrect. The question is the relative risk of the two vaccines, not the relative risk of vaccines versus other dangers. And it's noted that the switch will decrease cases of vaccine-caused polio—which is a good thing. This answer is out of scope.

Incorrect. It's established that OPV is the common vaccine in North America, which is the area this argument is about. This answer adds nothing relevant to the argument.

Incorrect. This answer suggests it very well might apply to both vaccines ("like most vaccines"). In an argument such as this one, a noted con will almost always need to be established as applying to only one of the two options.