OFFICIAL EXPLANATION


(B). The passage concludes that increased leisure time in the developed world causes an increase in the percentage of people diagnosed with clinical depression. To arrive at this causal conclusion, the argument must assume that alternative causes for this disparity are impossible.

(A) This statement weakens the hypothesis. If clinical depression were genetically transmitted, then the amount of leisure time would have no effect on the percentage of the population diagnosed with clinical depression.
(B) CORRECT. If individuals in the developing and developed worlds do not have equal access to accurate diagnostic procedures, it is possible that either frequent misdiagnoses or a lack of correct diagnoses causes the seeming disparity between the populations. Thus, for the argument to be valid, this assumption must hold true. Put another way, this assumption eliminates a possible outside cause (the difference in diagnostic techniques between the developing and the developed worlds).
(C) Nothing indicates that most leisure activities must be inherently boring. As long as more individuals in the developed world than in the developing world are experiencing boredom, the logic of the passage remains valid.
(D) This choice weakens the researchers' hypothesis. If fewer effective medications were available in the developing world, the incidence of clinical depression there should be higher than in developed countries.
(E) It is unimportant whether few residents of developing countries dedicate any of their time to leisure. The argument already states that residents of developed countries have increased leisure time relative to residents of developing countries, so this assumption is unnecessary.