Assumption Eliminate alternate models of causality The passage concludes that increased leisure time in the developed world causes an increase in the percentage of people diagnosed with clinical depression. For this causal conclusion to be valid we must eliminate alternate causes for this disparity.
Note: some questions of this type focus on eliminating reverse causality. That is, if the conclusion is that X causes Y (because X and Y are observed together), then one assumption is that Y does notcause X. Other questions focus on eliminating an outside cause. That is, if the conclusion is X causes Y (because X and Y are observed together), then another assumption is that Z (some outside force) does not cause Y. As it turns out, this question is of the latter type: eliminating an outside cause.
(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 the 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.