PT48, S4, Q25 Therapist: In a recent study, researchers

by **bbirdwell** Wed Dec 09, 2009 4:38 pm

25. (B)
Question Type: Identify a Flaw
Always be wary of study-based arguments that utilize statistics. Making invalid inferences from percentages is a common logical error on the LSAT. The form this usually takes is incorrectly shifting either between actual numbers and percentages, or between percentages of one whole and a different sort of whole. Here, we see the latter: 75% of the 60 problems studied cleared up within 50 weeks of therapy. The author then concludes that MOST people will only need 50 weeks or therapy. If we read too quickly or too un-critically, it is easy to conflate 75% with "most."

However, 75% refers to the number of problems studied. The conclusion refers to the percent of people being treated who will find that length of treatment adequate. Let’s assume that there were 1,000 people in the study. It is quite possible that the 75% , or 45, of the 60 problems that cleared up each only affected one person, for a total of 45 people (out of 1,000). While the remaining 25% (15) of the 60 problems that did NOT clear up within 50 weeks affected most of the people in the study (the remaining 955). Facing those numbers, it would be difficult to argue that 50 weeks of therapy is enough for MOST people!

Answer choice (B) is the crux of this argument-busting scenario _ any one of the 60 problems (i.e. one that did not clear up within 50 weeks) might afflict most people.

(A) is wrong because of the word "no." The argument says "most" problems will clear up within 50 weeks, not "all." Even if there is a problem that is incurable with 50 years of therapy, it still may be true that 50 weeks is sufficient for most people.
(C) is incorrect though tempting. We have no evidence that it takes more than 50 weeks to treat multiple conditions simultaneously. If we were to accept that there is a problem that affects most people in the study, it would seem to be one that is cured within 50 weeks of therapy, since the majority of people were cured within that timeframe.
(D) is out of scope. So what if some therapies are not proven? The therapies cited in the argument worked within 50 weeks for 75% of the conditions studied.
(E) is incorrect because, if anything, this would seem to support the conclusion. If it takes 50 weeks or less to treat people with an extraordinary number of problems, it would seem reasonable that it would take 50 weeks or less to treat people with fewer problems.