Q21 - People with higher-than-average blood levels

[mshinners]

Question Type:
Weaken

Stimulus Breakdown:
Homocysteine is correlated with Alzheimer's, so something that reduces homocysteine should help with Alzheimer's.

Answer Anticipation:
This is the classic correlation/causation flaw - don't get distracted by the extra step in the conclusion (vitamins/folic acid).
Purported cause: Homocysteine
Purported effect: Alzheimer's
To weaken causal relationships, we generally look for an alternative cause, a counterexample, or reversed causality. In medical questions, reversed causality has, historically, been the correct answer, so we should be on the lookout for an answer stating Alzheimer's increases homocysteine levels.

Correct answer:
(E)

Answer choice analysis:
(A) Too weak. Since the argument isn't absolute about the connection between these two (h levels being the only cause), "many" examples won't cut it.

(B) Out of scope. The conclusion is just about Alzheimer's. This answer would be more attractive if the conclusion was about overall health.

(C) Too weak. The argument doesn't tell us what level of homocysteine/B vitamins would be required to help with the disease, so even a level from inefficient metabolization could be enough.

(D) Out of scope. Tempting, though, because this seems to give an alternative cause (genetics). However, genetics doesn't preclude homocysteine levels being the culprit - maybe the bad genes impact homocysteine levels (or B vitamin levels), and supplements could still help.

(E) Bingo. This answer states that we reversed the causality, thus weakening the argument.

Takeaway/Pattern: For weaken questions about medicine, featuring causality, look for a reversal answer.

#officialexplanation