LSAT PT51, Section 1, Question 12, A study found that most of the strokes diagnosed by …

Why is (B) the answer and not (D)?

Roughly speaking, (B) makes an argument based on math. If it's likely there's a 50-50 chance of a stroke happening in either side of the brain, you'd expect doctors to diagnose a roughly similar number in either side. The study, however, found that most of the strokes diagnosed were only on one side. This means strokes on the other side had happened but were probably not being caught.

(D) is interesting but it's incomplete since it doesn't tell us how being different makes it harder to diagnose right-hand strokes. We're assuming that. If (D) had said the symptoms of right-side strokes are different and tend to be similar to those of other common ailments, it may have had potential.

- therctutor LSAT Tutoring